Journal of Archaeological Science 35 (2008) 2813–2823
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Journal of Archaeological Science
journal homepage: http://www.elsevier.com/locate/jas
Stone Age fishhooks – how were they dimensioned? Morphology, strength test,
and breakage pattern of Neolithic bone fishhooks from Ajvide, Gotland, Sweden
Carina Olson a, *, Karin Limburg b, Mikael Söderblom c
a
Osteoarchaeological Research Laboratory, Department of Archaeology and Classical Studies, Stockholm University, Lilla Frescati 7, SE-106 91 Stockholm, Sweden
State University of New York, College of Environmental Science and Forestry, Syracuse, NY 13210, USA
c
Sadelgatan 279, SE-194 72 Upplands Väsby, Sweden
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 January 2008
Received in revised form 26 April 2008
Accepted 14 May 2008
The late Stone Age Pitted Ware site at Ajvide, Gotland, in the Baltic Sea, Sweden, has revealed a large
deposit of fishbone and approximately 400 bone fishhooks, complete and incomplete. Cod (Gadus morhua), which is one of the most abundant fish species in the bone assemblage, was probably caught with
hook and line fishing. To investigate the fishhooks’ field of application, a morphological and morphometric study was performed on 384 available hooks. Two sets of replicas made of four selected original
fishhooks were submitted to a strength test. A breakage study of the incomplete hooks in comparison
with the strength-tested hooks was carried out in order to distinguish fresh breaks from dry breaks. It
seems that a certain morphology for fishhooks was preferred at Ajvide, indicating they were produced by
skilled craftsmen for special usage. The strength test showed that the hooks had a weight bearing capacity more than the average size of cod caught at Ajvide. Using results of these tests, we predicted that
the mean breaking strength of 46 intact Ajvide hooks was 96.6 26.1 (s.d.) Newtons (equivalent to
9.85 2.7 kg). The design of fishhooks changed somewhat over time, being slightly larger in the oldest
layers of the site. The breakage patterns of the hooks show that the bow was the most common area of
breakage. The design and weight bearing capacity of the hooks point to a specialized cod fishery from
boats in deep water.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
Neolithic bone fishhooks
Hook morphology
Hook sizes
Fish sizes
Material strength test
Breakage pattern
1. Introduction
In the middle Neolithic period, c. 3300–2300 BC (e.g. Berglund,
1999; Welinder et al., 1998), a coastal complex defined as the Pitted
Ware culture appeared in Sweden, Norway, Denmark and Åland/
Finland. In Sweden, the Pitted Ware sites have been found in the
coastal areas from Scania in the south (e.g. Burenhult, 1999;
Malmer, 2002; Welinder et al., 1998;) up to Ångermanland in
northern central Sweden (Björck, 1997; Färjare and Olsson, 2000),
as well as on the islands of the Baltic Sea (Janzon, 1974; Stenbäck,
2003; Storå, 2001; Österholm, 1989). The bone refuse from all these
sites indicates a similar coastal economy, based on fishing and seal
hunting (e.g. Edenmo et al., 1997; Ericson, 1989; Storå, 2001, 2002)
and a roughly similar diet (Eriksson, 2003; Lidén, 1995). Most Pitted
Ware site refuse faunas are dominated by seal bones, and where
preservation conditions are good, large amounts of fishbone are
also found, e.g. on the island of Gotland in the Baltic Sea, with its
calcareous soil and bedrock. Wild boar bones are also present in
rather large quantities at many Pitted Ware sites (Aaris-Sørensen,
* Corresponding author. Tel.: þ46 8161393; fax: þ46 8164476.
E-mail address: carina.olson@ofl.su.se (C. Olson).
0305-4403/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jas.2008.05.009
1978; Ekman, 1974; Rowley-Conwy and Storå, 1997; Hedell, unpublished data; Lepiksaar, 1974). Sites with Neolithic finds of bone
fishhooks on Gotland are Gullrum (Lithberg, 1914), Visby, Fridtorp
(Nihlén, 1927), Västerbjers (Stenberger, 1943), Ire (Janzon, 1974;
Ekman, 1974), and Ajvide (Burenhult, 1997; Österholm, 1989).
Ajvide on the southwestern coast of Gotland is exceptionally
rich in fishbone, and has also revealed the largest amount of bone
fishhooks among the Swedish Stone Age sites to date. The large
deposits of fishbone from marine species at Ajvide indicate the
importance of fish in the diet of the Ajvide people. A heavy dependence on marine proteins is supported by stable isotope
studies of human remains from Ajvide (Lidén, 1995; Lindqvist and
Possnert, 1997). The fish fauna from Ajvide consists of fresh-water,
marine and migratory species. Herring (Clupea harengus) and cod
(Gadus morhua) are the dominant species making 65% and 30%,
respectively, of the identified fish remains based on NISP. Other
fish species found at the site include pike (Esox lucius), perch (Perca
fluviatilis), flatfish (Pleuronectiformes), salmonids (Salmonidae),
cyprinids (Cyprinidae), whitefish (Coregonidae), and eel (Anguilla
anguilla) (Olson and Walther, 2007).
Archaeological finds show that hooks, nets and leisters (pronged
spears) have been used as fishing implements at Ajvide. The fisheries of Ajvide included species that stayed in or passed through the
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C. Olson et al. / Journal of Archaeological Science 35 (2008) 2813–2823
Fig. 1. Location of the study. Map showing Gotland in the Baltic Sea, and the location of Ajvide on the southwestern coast of Gotland, latitude 57 140 N, longitude 18 80 E. The map of
Gotland shows the shoreline from the end of the Middle Neolithic period. Modified from Österholm (1989).
deep waters of the open sea during migration, as well as species
that visited or resided in the littoral waters and in streams. Flatfish
and cyprinids confirm fishing during the warmer part of the year,
while the other species presented fishing possibilities more or less
on a year round basis (Olson and Walther, 2007).
The main aim of this study was to examine the fishhook design
to evaluate if they were manufactured according to specific morphological criteria, to maximize catch efficiency for particular
fishing strategies or species. In particular, we wished to test the
hypothesis that the hooks were designed for cod fishing on local
stocks. In this case, the hook morphology and strength should
match the size of the cod caught at Ajvide, for which we here
provide weight estimates from fish bones. By using modern replicas
in a strength test, we also investigated the hooks’ weight bearing
capacity. The strength test would shed light on the breakage patterns of the fishhooks and thus facilitate comparisons with the
breakage patterns of the original hooks in the Ajvide assemblage.
The breakage and fracture patterns of the archaeological hooks
were studied in detail to be able to distinguish fresh breaks (i.e.
breaks from the time of active use) from dry breaks (breaks that
occurred from the time of deposition until discovery) and also to
estimate the effect of post-depositional destruction. Preservation
issues may have affected the possibilities of evaluating the morphology of the hooks, and thus must be checked.
2. Material
transgression layer, separates the lower older layers 4 and 5 from
the upper younger layers 1 and 2. The layers correspond to 10-cm
thick technical (excavation) layers. The hooks investigated in the
present study derive both from graves and from layers 1 to 5 of the
settlement area.
2.2. The Ajvide fishhook assemblage
This is the largest assemblage of bone fishhooks from the Stone
Age in Sweden. Out of 384 fishhooks, 354 derive from the settlement area, and the remaining 30 originate from 22 different grave
contexts. The fishhook assemblage comprises of complete (n ¼ 54),
incomplete (n ¼ 327), and unfinished hooks (n ¼ 3). Nearly all
fishhooks from Ajvide are made of long bones, like the tibia of wild
boar (Fig. 2). A few are made of wild boar tusks, and possibly are
some also made of metapods of elk or moose. No composite or
stone hooks have been recovered at Ajvide, but there is one doublepointed gorge of bone with centrally placed grooves for attaching
a line.
2.3. Fishhooks selected for the strength test
Four original, intact bone fishhooks (Fig. 3) from the Ajvide
fishhook collection were selected to be copied and used in
a breaking strength test. The four original fishhooks seem to be cut
out of the tibia of wild boar (Sus scrofa). Wild boar is the most
common terrestrial mammal in the faunal material at Ajvide.
2.1. The site
Ajvide is located in Eksta parish on the southwest coast of the
island of Gotland in the Baltic Sea (Fig. 1). Comprehensive studies
and yearly excavations have been carried out at Ajvide since the
early 1980s (Burenhult, 1997a,b, 1999, 2002; Österholm, 1989). The
excavations have revealed an interesting complex of both settlement areas and a large burial ground. Considerable amounts of
animal bones, more than 7000 artifacts, and 2.5 tons of pottery
have been recovered from Ajvide so far. The main period of use was
between 3200 and 2300 BC (Burenhult, 1997). A transgression that
took place at ca. 2900 BC cal. submerged the site for a short period
of time and divided the cultural layers, which is of importance for
the stratigraphy and the interpretation of the site. Layer 3, the
Fig. 2. Ajvide fishhook made from a wild boar tibia. Measure from the proximal end of
the tibia to the bow of the fishhook ¼ 83.8 mm.
C. Olson et al. / Journal of Archaeological Science 35 (2008) 2813–2823
2815
Fig. 3. Original intact Neolithic fishhooks from Ajvide, Gotland, copied for strength test. From left to right: H1, H2, H3, and H4. Squares: 30 30 mm.
However, since there are occasional imported finds of both moose
(Alces alces) and elk (Cervus elaphus) at Ajvide, bone of these species
cannot be disregarded as raw-material. The long bones of the most
common mammal at Ajvide, the harp seal (Phoca groenlandica),
were not suitable for fishhook manufacturing due to their
morphology, but they were often used for the production of awls.
Our criteria for the selection were (1) that the hooks, in size and
morphology, should be representative for the Ajvide fishhook assemblage, (2) that hooks with holes and grooves for line attachment should be tested, and (3) that a comparison of raw-material
should be carried out, using bone tissue of two mammal species
(local and imported) that we knew were available at Ajvide during
the Neolithic.
The original fishhooks H1 and H4 are equipped with a hole and
a groove for attaching the fishing line. On both these hooks the hole
diameter decreases towards the center of the shank, showing that it
was drilled from both sides. H2 and H3 lack holes, but are equipped
with grooves for line attachment. H2 has two grooves and H3 has
one groove on each side of the head of the shank. The upper ends of
the shanks of H2 and H3 include cancellous bone, while H1 and H4
are made solely of compact bone.
The raw-material for the replicas comes from a captive population of wild boar from the Åland Islands in the northern part of
the Baltic Sea, and from moose from the mainland of central
Sweden. Two sets of four replicas each were made. One set of
replica hooks was made from wild boar bone (designated with
‘‘-wb’’) and the other set was made of moose bone (designated with
‘‘-m’’) (Fig. 4).
3.1. Manufacturing the replicas
The fishhook manufacturing began with preparing the rawmaterial. The selected limbs were stripped off and cleaned of skin,
sinews, marrow, and the periosteum. This was done while the
material was fresh, to avoid the fat affecting the bones. Boiling the
bones, which may be a simpler way to clean them, is more time
consuming, and could also impair the special qualities of the raw
bone, such as strength and elasticity. After the preparation and
cleaning were carried out, the bone element was cut in two, and the
3. Methods
All 384 available hooks from the Ajvide fishhook assemblage
from graves and three chronological levels of the cultural layer
were morphologically analyzed. We measured eight different parameters (to the nearest 0.01 mm) including overall length, bow
height and width, point length, type of line attachment, gape, and
gripping angle (Fig. 5a and b). We identified and classified type of
fracture for the incomplete hooks. Three of the incomplete hooks
were not measured since they are in an ‘‘unfinished’’ state, meaning, not separated from the raw-material.
Fig. 4. Replicate fishhooks constructed of moose (m) and wild boar (wb) bone showing
fractures. Scale same as in Fig. 2.
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C. Olson et al. / Journal of Archaeological Science 35 (2008) 2813–2823
Fig. 5. (a,b) Fishhook morphology and measured parameters. (a) A ¼ fishhook head
incl. line attachment area, B ¼ shank, C ¼ bow, D ¼ point. (b) Fishhook parameters that
were measured: OL ¼ overall length, MBH ¼ maximum bow height, MBW ¼ maximum
bow width, PL ¼ point length, GAPE ¼ hook gape, GA ¼ gripping angle.
when the hook is just penetrating the skin of a fish, while loading at
the bottom of the bow would rather emulate the case when the fish
is already hooked. Since the hooks are much thicker at the bow
than elsewhere, this indicates that rupture often occurred in this
area, and that is likely due to bending moments from forces close to
the tip. Of course, under actual usage conditions, the load is distributed over the hook and the force on different parts of the hook
varies during the catch. Considering this, it was assumed that
loading close to the tip, avoiding point forces, would be adequate.
Thus a small metal cylinder (nut) was threaded over the hook’s tip
and the external force was applied to that cylinder some millimeters from the very tip. The hooks were fixed at their opposite ends
to the testing machine, using parts of a cord.
Loading equipment. The tests were run in a universal servo-hydraulic material testing machine, MTS load frame 50/100 KIP,
model 309.03, and INSTRON 8500þ digital control. A HBM load cell,
model U2B 0.5 kN #H01092 was used to measure the applied load.
The piston position was indicated by an integral linear variable
differential transformer (LVDT). Load and displacement were stored
in a connected PC.
3.3. Breakage pattern of Neolithic hooks
part intended as raw-material for the replica was selected. The
hook manufacturing consisted of a combination of fine cutting,
scraping, and grinding. As the project did not include the use of
authentic tools, steel-edged tools and grinding cloths were used,
but the procedure would have been similar if flint-edged tools and
sandstone had been used. The holes in the upper part of the shank
of hook H1r-m, H1r-wb, H4r-m and H4r-wb were drilled from both
sides with a bow-drill. The drill was made of round steel. The
pointed end of the round steel was cold forged into a cutting edge.
The copies are almost identical to the originals. There are only diminutive measurement discrepancies which are considered to not
affect the strength test in any significant way (Table 1).
3.2. Material strength test
In the purpose to find out the weight bearing capacity of the
selected fishhooks from Ajvide, two sets of replicas, consisting of
four hooks each, were subjected to tensile strength testing at the
Department of Solid Mechanics, KTH Royal Institute of Technology
in Stockholm.
3.2.1. Load application
The position of the applied loads is of main importance. Loading
at the very tip would result in lower breaking force than loading at
the bottom of the bow. Loading at the tip would emulate the case
To gain more insight into the hook and line fishing technology at
Ajvide, we studied the fracture areas of the incomplete hooks in
order to detect the fresh breaks, and to learn how the fishhooks had
ruptured during fishing. Three criteria of fracture were used for
identifying and distinguishing fresh breaks from post-depositional
breakage of dry bones (Johnson, 1985; Outram, 2001, 2002). A
fracture is identified and classified from (1) the fracture outline
(shape), (2) fracture angle, and (3) fracture texture (smooth or
rough). Our observations of the Ajvide fractures corresponded well
with the classification of fresh and dry breaks made by Johnson and
Outram, even if those did not include bone fishhooks. For the Ajvide
hooks, we define fresh breaks as having a smooth fracture texture
and mostly a sloped fracture area with rather sharp edges, while
the dry breaks often have a more straight fracture angle, rough
fracture texture, and rather blunt edges.
3.4. Cod sizes and weights at Ajvide
Methods for size estimations of archaeological remains of prehistoric fish have been established by a number of researchers
(Bødker-Enghoff, 1983, 1994, 1995; Casteel, 1976; Lepiksaar and
Heinrich, 1977; Morales and Rosenlund, 1979; Wheeler and Jones,
1989). Size estimates (maximum length) of cod at Ajvide have been
presented earlier based on measured otoliths (ear stones) and
Table 1
Parameter values of original and replicate fishhooks selected for the strength test
ID
Context
Hook no.
OL (mm)
MBH (mm)
MBW (mm)
PL (mm)
Hole/groove
HI Ø (mm)
Gape (mm)
GA
Weight (g)
Ultimate load
30826
30826
30826
CL
CL
CL
H1
H1r-m
H1r-wb
51.29
51.35
51.55
10.87
11.27
11.05
12.88
12.95
12.88
24.27
24.28
24.79
Hole
Hole
Hole
3.74
4.11
3.65
10.20
10.22
9.59
19
19
15
2.94
3.4
3.7
Original
109 N
106 N
30447
30447
30447
G6b
G6b
G6b
H2
H2r-m
H2r-wb
51.41
51.49
51.01
7.55
7.55
7.91
13.34
13.78
13.79
25.04
25.88
25.93
Groove
Groove
Groove
11.01
10.60
10.48
20
17
20
2.68
2.97
3.01
Original
86 N
106 N
30511
30511
30511
G9
G9
G9
H3
H3r-m
H3r-wb
62.28
62.28
62.01
9.08
9.16
9.04
11.24
11.24
11.22
29.46
29.38
29.39
Groove
Groove
Groove
11.82
11.83
11.74
20
20
17
2.13
2.45
2.62
Original
57 N
60 N
34544
34544
34544
sf G21
sf G21
sf G21
H4
H4r-m
H4r-wb
52.04
51.54
52.09
10.13
10.17
9.38
14.45
14.57
14.12
31.5
31.58
31.51
Hole
Hole
Hole
11.12
11.50
10.06
14
18
13
2.98
3.38
3.03
Original
69 N
82 N
3.81
3.81
3.66
CL ¼ cultural layer, G ¼ grave, sf ¼ sieve find, OL ¼ overall length, MBH ¼ maximum bow height, MBW ¼ maximum bow width, PL ¼ point length, GAPE ¼ hook gape,
GA ¼ gripping angle.
C. Olson et al. / Journal of Archaeological Science 35 (2008) 2813–2823
vertebrae (Olson et al., 2002; Olson and Walther, 2007). In the
present study, the weight (g) of codfish caught at Ajvide was backcalculated from regression relationships developed between body
length and sizes of preserved hard parts (otoliths and vertebrae).
We extrapolated weights of cod from a modern-day length–weight
relationship derived from Baltic Sea cod (Marine Research Laboratory, Lysekil, unpublished data), using the following formula:
weight ¼ 0.0039621(TL)3.2375, N ¼ 40, R2 ¼ 0.99. TL (total length) is
the maximum length of the cod with mouth closed and tail fins
squeezed together (Casteel, 1976). The calculated weights supplied
information about approximate weights of the cod captured at
Ajvide, and were compared with the loads used in the strength test.
3.5. Statistics
Oneway ANOVAs were calculated on all fishhook parameters
with a known layer affiliation (layers were the categorical variable)
to test whether there were any significant changes in design over
time. Post hoc tests (Fisher’s Least Significant Difference) were
made, and an alpha of 0.05 was used as the level of significance. In
addition to this, the correlation (Pearson’s r) between all combinations of the fishhook parameters was calculated to see if they
correlated proportionally within the hook assemblage regardless of
hook size. These analyses were designed to test whether or not
a homogeneity of design, indicating a specialized fishing technology was statistically detectable.
To help understand the factors that promoted increased loadbearing strength, parameters from the eight replica hooks were
examined by regressing load (newtons) on individual parameters,
and a principal components analysis (PCA) confirmed which combination of variables had strong effect on load. From this, a multiple
linear regression was developed and used to predict potential loads
that could have been borne by original hooks; this last analysis was
performed on intact hooks from layers 1 to 5.
4. Results
4.1. Fishhook morphology
The manufacture of the hook replicas required a detailed examination of the original fishhooks. The four original fishhooks had
been carved out of the flat side of the bone and followed the natural
curvature of the bone surface. All hooks were carefully worked and
have finely polished surfaces, although on close examination it is
possible to detect parts of the hooks that carry traces of harsher
working. Grooves for attaching the fishing line are more common
than holes in general, but the frequency of holes decreases over
time, from 45% in layer 4 þ 5 to 20% in layer 1 þ 2. Most hooks have
barbed points (82 of 91 intact points). All bows of the hooks are
more or less strengthened, which means the bone material in the
bow is thicker than elsewhere in the hook. The hook morphology of
all sizes of hooks is similar, except for a few among the smallest
Table 2
Mean parameter values, Ajvide fishhooks
Fishhook
Complete þ incomplete originals
Strength-tested replicas
Parameter
Number
Mean
s.d.
Number
Mean
s.d.
OL
MBH
MBW
PL
Gape
GAa
134
211
120
91
61
53
53
9
13
28
10
21
8.5
2.1
2.4
5.7
1.8
8.7
8
8
8
8
8
8
54
9
13
28
11
17
4.9
1.3
1.3
3.0
0.8
2.5
Parameter mean values for complete þ incomplete, and strength-tested hooks.
OL ¼ overall length, MBH ¼ maximum bow height, MBW ¼ maximum bow width,
PL ¼ point length, GAPE ¼ hook gape, GA ¼ gripping angle.
a
One hook holding a GA of 10 is not included.
2817
Table 3
P-values for Ajvide fishhook measure categories from three chronological levels
(i) Level
(j) Level
OL
MBH
MBW
PL
GAPE
GA
Layer 1 þ 2
Layer 3
Layer 4 þ 5
Layer 4 þ 5
0.043*
0.046*
0.949
2.720
117
119
0.880
0.429
0.352
0.471
182
184
0.717
0.570
0.777
0.168
99
101
0.532
0.091
0.209
1.497
74
76
0.869
0.277
0.290
0.716
46
48
0.322
0.358
0.910
0.453
40
42
Layer 3
F-value
df
n
Statistic method ¼ Oneway ANOVA, post hoc Fischer LSD. * ¼ Significant at alphalevel 0.05.
hooks, that have a design that differs from the rest of the hooks in
the assemblage. Some of these are proportionally short, while
others have shanks (perhaps reworked) that are almost as short as
the point length.
The overall lengths (OL) of 134 measurable (complete and incomplete) hooks range from 30 to 79 mm, with a mean value of
53 mm (s.d. ¼ 8.5). Point lengths greater than 50% of the overall
length (OL) are most common. The point lengths of 91 measurable
hooks range from 11 to 40 mm. The mean value is 28 mm
(s.d. ¼ 5.7). The maximum bow heights (MBH) of 211 measurable
hooks range from 6 to 20 mm. The mean value is 9 mm (s.d. ¼ 2.1),
making 13–20% of the OL, and 69% of the maximum bow width. The
maximum bow widths (MBW) of 120 measurable hooks range between 6 and 20 mm. The mean value is 13 mm (s.d. 2.4). The gapes,
(i.e. the horizontal distance between the top of the point and the
shank) of 61 measurable hooks range between 5 and 15 mm, with
a mean value of 10 mm (s.d. 1.8). Except for one hook of a very
special design, showing a gripping angle (GA) of 10 , the gripping
angles of 53 measurable (intact) hooks vary between 10 and 63 .
The mean value is 21 (s.d. 8.7). The mean values for the hooks
selected for the strength test are – overall length: 50 mm, maximum
bow height: 9 mm, maximum bow width: 13 mm, point length:
27 mm, hook gape: 10 mm, and gripping angle: 21 (Table 2).
Statistical analyses revealed that only one design parameter
changed over time. The overall length (OL) showed a significant
difference (p ¼ 0.043) between layer 4 þ 5 and layer 1 þ 2, and also
between layer 3 and layer 1 þ 2. (Table 3). The hooks were larger in
layers 3–5, than in layer 1 þ 2. Moreover, there are tendencies that
point length, maximum bow width, gape and gripping angle were
slightly larger in the upper, younger layers, even if these changes
are not statistically significant. The maximum bow height proved to
be the most static measure, and showed only very small differences
among the layers (Table 4).
The correlation between the different measure categories of the
fishhooks, calculated from the complete hooks in the hook assemblage, was statistically significant for most of the parameters,
only MBH-gape, MBH-GA, MBW-GA and PL-GA did not exhibit
significant correlations (Table 5). That the MBH did not correlate
with the gape and gripping angle seems logical, since the value of
the bow height cannot affect the value of the gape and gripping
angle, while the lack of correlation between the MBW-gripping
angle and the point length-gripping angle is more difficult to
Table 4
Parameter mean values of fishhooks from three chronological levels
Unit
Parameter
Layer 4 þ 5
Mean
s.d.
Mean
s.d.
Mean
s.d.
mm
mm
mm
mm
mm
Degrees
OL
MBH
MBW
PL
GAPE
GA
54.55
9.46
12.61
26.12
9.24
15
8.35
2.39
2.57
7.37
2.01
12.94
54.43
9.1
12.78
28.33
9.98
16
7.85
1.86
2.33
5.69
1.6
6.7
50.72
9.15
12.98
29.3
10.08
20
8.53
1.98
2.32
5.01
2.03
10.59
Calculated from 577 measures.
Layer 3
Layer 1 þ 2
Total
number
120
185
102
77
49
42
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C. Olson et al. / Journal of Archaeological Science 35 (2008) 2813–2823
Table 5
Ajvide complete fishhooks
Parameter
r
p
Significance
OL–PL
OL–MBH
OL–MBW
OL–gape
OL–GA
MBH–MBW
MBH–PL
MBH–gape
MBH–GA
MBW–PL
MBW–gape
MBW–GA
PL–gape
PL–GA
Gape–GA
0.662
0.571
0.323
0.366
0.275
0.402
0.578
0.244
0.128
0.658
0.472
0.140
0.553
0.023
0.535
0.000
0.000
0.017
0.006
0.044
0.003
0.000
0.076
0.356
0.000
0.000
0.314
0.000
0.871
0.000
<0.01
<0.01
<0.05
<0.01
<0.05
<0.01
<0.01
<0.01
<0.01
<0.01
Fig. 6. Predicted weight bearing loads (newtons, means þ s.e.) of 46 intact fishhooks
from Ajvide, by chronological layer. N for each layer is written on the column. Eight
intact hooks from unknown time horizons are not included in the figure.
<0.01
The correlation (Pearson’s r) between different parameter categories (n ¼ 54).
explain, since these measures are closely related and ought to affect
one another. Although there is a variation in the size between the
hooks, the rather strong correlation between most of the parameters indicates that the hooks were morphologically proportional.
4.2. Strength test and breakage of hook replicas
The test-hooks ruptured either in the bow or close to that
(Fig. 4). The ultimate loads range from 57 to 109 N (Table 1). The
strength of the hooks is enough to bear 6–10 kg dead weight in air.
The ultimate load is due to three groups of factors: the geometry,
the material and the loading. The possible geometry may be restricted by factors that influence the fishing efficiency. Bone is an
anisotropic material with a strength that varies with the loading
direction. The precise loading position is unknown in advance. Thus
it is impossible for the maker of the hooks to choose the optimal
geometry for best strength in all individual cases. A compromise
based on experience is necessary. The design of the tested hooks
did not seem to affect the rupture areas as much as the difference in
raw-material. All the hooks made of moose bone ruptured in the
center of the bow, while only one made of wild boar had a center
bow fracture, and the remaining three ruptured in connection to
the bow area. The raw-material comparison also showed that three
of the four fishhook types (H2, H3 and H4) had higher Newton
values when made of wild boar bone. Only hook type H1 manufactured of moose bone withstood somewhat more load than H1
made of wild boar bone (Table 1).
4.3. Predicted loads of hooks from Ajvide
Regression and PCA revealed that three parameters correlated
strongly with load-bearing strength in the replica hooks. Two of
these parameters, hook gape and point length, were inversely related to load, whereas hook weight was positively correlated. A
multiple regression with load as the dependent variable and these
three parameters as independent variables yielded the following
predictive equation:
38.8–173.8 N (3.9–17.7 kg). ANOVA tests of predicted load by burial
layer showed similarity of loads across time, with the possible exception of layer 5 which had somewhat higher mean loads (Fig. 6).
However, given that only two intact hooks were found in layer 5, it
is difficult to draw conclusions.
4.4. Fracture pattern of hooks from Ajvide
Only 14% of the Ajvide fishhooks we studied are complete (intact), and the remaining 86% (incomplete hooks) have one or two
fractures. There are 10 locations of fractures registered: four single
fracture locations (head, shank, bow and point) and six double
fracture locations (head þ bow, head þ shank, head þ point,
shank þ bow, shank þ point, and bow þ point). The surface of the
rupture areas of the replica hooks and the originals is rather similar,
but the original hooks tend to show a more sloped or angled fracture area. Single fractures are most common and make 77% of the
total amount of fractures. Shank fractures predominate (33%)
somewhat over bow fractures (32%), both in settlement and grave
contexts. Point fractures made 10% and head fractures only 2% of
the total number of fractures. Double fractures were registered on
23% of the hooks, of which there is a slight dominance of the
combination of shank þ point fracture (Table 6).
Fresh breaks were noted on 39% and dry breaks on 20% of the
incomplete hooks. The remaining fractures (indeterminate 41%)
were difficult to assess, either due to the state of preservation or
due to the ambiguity of the ruptured surface (Table 6). The fracture
texture of the fresh breaks proved to be rather smooth, like those of
the tested hooks. The edges of the fresh breaks were sharp. The
fracture surfaces of the dry breaks were rough and the edges in
general not as sharp as the fresh breaks. Like the tested hooks, bow
fractures dominate among the original hooks with fresh breaks.
Shank fractures are the most common type of fracture in the group
of dry breaks, and more than 50% of these fractures were caused by
post-depositional processes.
4.5. Cod sizes
The reconstructed weights, obtained from 486 otoliths and
vertebrae of the Stone Age cod from Ajvide (Fig. 7) show that 40% of
Load ðNÞ ¼ 276:8636 3:0823 ðpoint lengthÞ
12:5851 ðgapeÞ þ 9:3323 ðweightÞ
Table 6
Number of fractures per breakage category from all contexts
Breakage HF HF&BF HF&SF HF&PF SF
R2 ¼ 0:90; F3:4 ¼ 12:33; p < 0:05:
We used this equation to predict the loads potentially borne by
46 intact hooks found at Ajvide. Predicted loads had a normal
distribution with a mean of 96.6 N (9.85 kg) 26.1 (s.d.), range
Fresh
Dry
Indet
Sum
%
2
1
5
8
2
3
3
1
2
6
8
2
1
6
7
2
SF&BF SF&PF BF
36
26 4
46 16
108 20
33 6
5
23
28
9
BF&PF PF Sum %
75
6 9
21 3
102 12
31 4
13 138
42
10 52
16
8 137
42
31 327
10
100
HF ¼ head fracture, SF ¼ shank fracture, BF ¼ bow fracture, PF ¼ point fracture.
C. Olson et al. / Journal of Archaeological Science 35 (2008) 2813–2823
2819
taken place from boats in deep waters which large fish occupy. They
also noted a change in design where the older hooks from the
Mesolithic usually were U-shaped, while those of later periods
were more V-shaped and had longer shanks and a differently
designed upper shank where the line was attached. In Norway,
Stone Age fishhooks confirm a variety of fisheries by the many
different sizes and forms of hooks found there. A characteristic of
the Norwegian hooks is, that the design of is often of such a distinctive feature that the hooks can be connected to a certain site
(Bakkevig, 2003). Tegermark (1997) made a study of the distribution of fishhooks within the Ajvide site area (n ¼ 261 available at
the time). He concluded that 9% of the hooks derived from grave
contexts and 91% from the cultural layer. These figures remain the
same after our recent study. He also made a morphological survey
of the hooks and concluded from their size and form that they
would have been suitable for line fishing for cod. However, all
previous studies lack a detailed investigation of the morphology
and use of the fishhooks.
5.1. Morphology
Fig. 7. Cod weights predicted from vertebrae and otoliths from Ajvide cod (n ¼ 486).
the captured cod weighed less than 2 kg, 52% weighed 2–3.9 kg,
and 8% weighed 4–7 kg. Consequently, the fishhooks from Ajvide
were well dimensioned to carry the sizes of the captured fishes,
when one considers that live weight puts more load on a hook than
dead weight.
No statistically significant chronological change in cod size was
observed. The largest and the smallest individuals were found in
the oldest level. However, even if not statistically observable, there
is a tendency of an increase of cod mean size over time. The sizes of
the fishhooks show that both the largest and the smallest ones
were found at the transgression layer (layer 3), but, the highest
hook mean size was found at the oldest level where also the largest
cod were found (Table 7).
Interestingly, a strong correlation between mean, minimum,
and maximum hook and cod lengths is apparent, with cod lengths
being approximately 10 times that of hook overall lengths (cod
length ¼ 10.37 cm, hook length ¼ 0.59 cm; R2 ¼ 0.93). Frequency
distributions of all cod and hook lengths are strikingly similar
(Fig. 8), offset by a factor of 10, suggesting a correspondence.
5. Discussion
When comparing the Ajvide fishhooks with contemporaneous
fishhooks from other Pitted Ware sites on Gotland (e.g. Janzon,
1974; Schnittger and Rydh, 1940; Stenberger, 1943), and Öland in
the Baltic Sea (Schulze, 1973), the resemblance in design is obvious.
Stenberger (1943) and Janzon (1974) examined Gotlandic fishhooks
and their use. Janzon also classified hooks based on the morphology
of the line attachment area and the point. Lekholm (1951) studied
prehistoric hooks from Scania in southern Sweden and discussed
their field of application by the way they were constructed. Hernek
and Jonsson (2003) dealt with fishhooks from the southwestern
coast of Sweden. They concluded that hook and line fishing had
The similarities in measurement values for both complete and
incomplete hooks of the fishhook assemblage from Ajvide support
their homogeneity. The average Ajvide fishhook has a length of
53 mm, bow height of 9 mm, bow width of 13 mm, point length of
28 mm, gape of 10 mm and a gripping angle of 17. Grooves are
more common than holes for attaching the line. Grooves dominate
in all periods, and the occurrence increases over time while the
frequency of holes decreases. Since head fractures are so few, the
reason for the decrease is probably not related to stress, but perhaps to the manufacturing process. Grooves may have been less
time consuming to make, but had apparently the same functional
qualities as holes. The strengthened bows occur in all periods,
probably due to their high exposure to stress, which is shown in the
breakage study and the strength test. The design of a fishhook is of
importance for its function, and the morphology can to a certain
extent reveal its field of application. An interesting detail of the
Ajvide fishhook design, from a manufacturing view, is that the inner bow of many hooks from Ajvide including hook H2, seems to
have been bored, instead of carved. Judging by the surface of the
walls inside the holes, a high revolution drilling-tool must have
been used, perhaps a bow-drill. This was a procedure that would
have facilitated the manufacturing process considerably. This
method, known within prehistoric technology (e.g. Chaussonet,
1995; Craig, 1967; Johansson, 1993), was also used on the Stone Age
Scanian Fishhooks described by Lekholm (1951).
5.2. Fishing technology
Considering the location of the Ajvide site, on the seashore,
facing both a lagoon with shallow water and the open sea, various
kinds of capturing methods must have been used for the different
fish species inhabiting these waters. From the recovered fishbone
material, it can be anticipated that fish species like herring, flatfish,
pike, perch, salmonids and eel were mostly caught with stationary
Table 7
Comparisons between cod and fishhook weights and cod total length (TL) and fishhook overall length (OL)
Parameter
Cod w (g)
Hook w (g)
Cod (cm) TL
Hook (mm) OL
Layer 4 þ 5
Layer 3
Layer 1 þ 2
Total number
Min
Mean
Max
Min
Mean
Max
Min
Mean
Max
218.1
0.4
29.1
36.2
1952.9
2.0
54.7
54.6
6728.9
4.1
84.0
76.7
509.2
0.4
37.9
30.5
1892.5
2.6
55.1
54.4
4576.6
5.6
74.6
79.0
307.8
0.9
32.4
34.0
2201.9
2.2
56.6
51.0
5130.7
2.9
75.0
70.3
Minimum, mean and maximum values from three chronological levels.
366
46
486
120
2820
C. Olson et al. / Journal of Archaeological Science 35 (2008) 2813–2823
Fig. 8. Cod and hook size distributions (n ¼ 477 cod, 134 hooks).
traps, nets and sometimes leisters. However, for cod, which seasonally stay in coastal waters, but not often in the immediate vicinity of the shore, methods such as hook and line fishing would be
more efficient. The large amount of cod bones and fishhooks at
Ajvide certainly point to the importance of this fishing method. The
fact that the size of the hooks decreased slightly over time reflects
some kind of change. Whether it was due to an improved fishing
technology, a more specialized fishery or other causes, this indicates a change in the subsistence economy. A further indication of
such a change is found in the mammal remains from the same time
span at Ajvide. They show that seals decrease, while the amount of
wild boar increases over time (Lindqvist, 1997; Rowley-Conwy and
Storå, 1997; Storå, 2001).
At Ajvide marine, diadromous (migratory) and fresh-water fish
species were consumed, although cod and herring were the two
dominant species. This makes Ajvide somewhat different from
coastal sites having access only to marine species, which may to
a certain extent have affected Ajvide’s fishhook material, in terms of
size, form, and function. There is always the possibility that the
hooks from Ajvide occasionally were used for species other than
cod, such as cyprinids, perch, pike and salmon. However, using
stationary fishing equipment for fishes active in shallow lagoon
waters, creeks or streams were presumably more productive and
energy saving than using a hook and line (e.g. McQuade and
O’Donnell, 2007; Pedersen, 1995). Younger codfish may occasionally have been caught in fish traps or nets in shallower waters along
the coastline, as described by Bødker-Enghoff (1986, 1989, 1994,
1995) in her studies of Danish Mesolithic fishbone materials.
Pickard and Bonsall (2004) also studying Mesolithic fishing in
Europe, only found evidence for deep-sea fishing in regions where
deep water was found close to shore. They further comment that
according to ethnographical data, offshore subsistence fisheries
were practiced only where there was limited availability of terrestrial resources, a fact that agrees well with the restricted land
mammal fauna on Gotland.
Based on the size and form of the majority of the fishhooks from
Ajvide, and the estimated sizes of the recovered cod from the site,
we believe that the hooks were mainly intended for fishing gadids
in deep waters some distance from the settlement. Our definition of
hook and line fishing in this study is: a fishery with a hook attached
to a hand line, hanging more or less vertically in the water down
from the boat. We suggest the boats were some kind of dug out
canoes, perhaps of a stable outrigger type like those used in the
South Pacific (e.g. Österholm, 1997). We assume the fishery took
place at depths of approximately 50 m or more, about 5–6 km away
from the shore.
The penetration power of the hook is closely related to its design. A hook with a short shank and a broad gape needs greater
power to penetrate the mouth of the fish than a long shank with
a small gape. For hook and line fishing bent hooks can penetrate the
fish more efficiently than a straight hook (Broman, 1979). This fits in
well with the design of the Ajvide hooks which are long, have
rather small gapes, and mostly a point length area that is more or
less bent in relation to the shank. Consequently, we conclude that
the Ajvide hooks were designed for the use of low penetration
power during hook and line fishing.
There are no remains of the lines that were used together with
the hooks from Ajvide. The strength, elasticity, and material of the
fishing lines that once were attached to the fishhooks are unknown
variables. However, prehistoric finds and ethnographic studies
show that the manufacturing of lines, strings and ropes was
common in low-technology communities (e.g. Andersen, 1985;
Murdoch, 1892; Stewart, 1982). Lines could be produced both from
animal and vegetable materials. The bast of linden-tree (Tilia spp.)
has, for example, been used for making lines in temperate areas,
like the uniquely preserved line from the Mesolithic site Tybrind
Vig in Denmark (Andersen, 1985). In arctic and sub-arctic areas,
with poor access to deciduous forests, long, braided sinews
(sometimes more than 20 m) were used for purposes from retrieving lines for harpoons to reinforcements on bows (Callahan,
1991; Murdoch, 1892). When sinews are braided, they withstand
the dissolving effect of water. Another vegetable material besides
linden bast that could have been used at Scandinavian latitudes is
nettle (Urtica dioica) fibre, which was frequently used by the indigenous fishers at the northwest coast of USA and Canada (e.g.
Stewart, 1982). The different attachment areas for the lines are
considered to have had little or no effect on the fishing techniques,
while the strength of both the hook and the line was a determining
factor. Salls (1989) tested the strength of fibre plant lines similar to
those used in prehistoric California to see if they were strong
enough to carry the sizes of different fish species found at excavations in southern California. His results revealed that the native
fibre plant lines probably would have been limited to catching fish
weighing 10–20 pounds (5–9 kg), which agreed well with the archaeological record showing that native fishermen mainly utilized
these fish sizes in the nearshore habitats.
Unaware of what lines were used at Ajvide, one could argue that
the lines were the weak point, and the cause of the lack of large cod.
However, the finds of harpoons at Ajvide indicate they must have
had lines strong enough for harpooning all the seals found at the
site. Therefore, it is not likely they lacked the knowledge how to
make fishing lines sufficiently strong for their purposes, but, despite this observation, we cannot totally exclude the possibility that
the lines sometimes broke during fishing.
Our study demonstrates that fishhooks from Ajvide had the
capacity to hold very large fishes with line fishing. Even if there is
no evidence yet of cod body lengths over 900 mm (comparable to
a weight of 6–7 kg) in the osteological material from Ajvide, it is
still possible that these sizes of cod were caught at times. One
cannot disregard that the fishhooks were, in their ultimate
strength, made to handle the occasional large codfish. One must
also consider that a fishhook in everyday use is exposed to a variety
of stress factors that cannot be simulated in a test-bench in air. Such
stress could be caused by the movements of the fish in relation to
the boat’s vertical and horizontal movements, the elasticity of the
line, the way the point of the hook penetrates the mouth or body of
the fish, and the handling of the fish when taken out of the water.
Therefore, it needs to be considered that the hooks may have
ruptured at lower loads when exposed to higher stress in water. We
assume the fishers at Ajvide were well aware of all the stress affecting factors, and had them in mind when they manufactured the
hooks, which could explain the high weight bearing capacity
proven by the strength test.
The somewhat stronger fishhooks made of wild boar bone
compared to those made of moose bone, may indicate a difference
C. Olson et al. / Journal of Archaeological Science 35 (2008) 2813–2823
in bone strength between the hooks, even if not statistically demonstrated. The hooks made of moose bone, all consisted of compact
bone, while those made of wild boar bone included some cancellous bone since the porous upper part of the wild boar tibia shaft
had to be used. The compact area of the tibia was not large enough
for cutting out a complete hook. This however, did not affect the
outcome of the strength test as all hooks broke in or close to the
bow area. We certainly believe that the Stone Age craftsmen were
well aware of how different bone tissue affected the function of
their tools and that the manufacturing followed well developed
strategies. The availability of raw-material at Ajvide was probably
good, and it is not likely that fishhooks were made from bone of
dubious quality.
The use of fracture analysis methods for unworked bone
elements (Johnson, 1985; Outram, 2001, 2002) proved to be applicable to bone artifacts, in this case with bone fishhooks. The
fracture analyses showed that the fresh fractures of the original
fishhooks were more sloped than the fresh fractures of the replicas,
presumably owing to the difference between real fishing and static
load stress. Both replicas and originals showed a smooth texture of
the fracture surfaces. The breakage pattern gives an indication
about a number of weak parts of the hooks. The bow (n ¼ 75) and
shank (n ¼ 36) hold the highest record of fresh fractures while the
point (n ¼ 13) and head or line attachment area (n ¼ 2) were not as
often fractured. The variety of fractures displayed on the tested wild
boar hooks agrees well with the fractures occurring on the original
fishhooks from Ajvide, which were also primarily made of wild
boar bone. The fact that the rupture areas are mostly in or close to
the bow, explains why this exposed area of the hook was almost
always strengthened in the manufacturing process. Although the
bows were strengthened, they show the highest amount of fresh
breaks, indicating this was still the weakest part of the hook.
However, to further strengthen the bow would perhaps have affected the functional qualities of the hook. Allen (1996) discussed
functional and stylistic traits on fishhook assemblages from
a number of island sites in the South Pacific, where she also concluded the bend was the weakest part of one-piece hooks. In the
South Pacific, large one-piece hooks decline while two-piece hooks
increase in abundance over time. The explanation to this may be
the functional superiority of the two-piece hook, where ‘‘the weak
bend region is effectively ‘broken’ and then reinforced with a flexible lashing’’ (Kirch ref. to in Allen, 1996). As earlier indicated there
are no traces of two-piece hooks at Ajvide, leaving an eventual
similar development in fishing technology unknown.
There is a dominance of bow fractures below the transgression
layer (layer 3). Within the transgression layer shank fractures and
bow fractures show almost equal amounts, while shank fractures
clearly dominate above the transgression layer. It is also obvious
that the incidence of both shank and point fractures increases over
time (Fig. 9). A high post-depositional destruction is indicated by
the increased occurrence of dry and indeterminate breaks within
2821
Fig. 10. Breakage category per chronological level (n ¼ 279).
the youngest layers (Fig. 10). A similar indication of fracturing is
described for wild boar (Outram, 2001, 2002) and bird bones
(Mannermaa and Storå, 2006) from the fauna at Ajvide, where dry
fractures increase and fresh fractures decrease towards the upper
layers of the stratigraphy. It is obvious that post-depositional
breakage (dry breaks) may mask the original fracture patterns of
the hooks. However, since we, in this case, carried out the strength
test of the replicas and the breakage study, we could distinguish the
fresh breaks from the dry breaks, and reveal the bow as the weakest
part of the fishhook, in spite of the higher occurrence of shank
fractures among the archaeological hooks.
6. Conclusions
The Stone Age site of Ajvide on Gotland, Sweden yielded a remarkable collection of fishhooks indicating the importance of
fishing and fishhook production. The homogeneity in size and form
of the fishhooks points to a planned manufacturing. Hook morphology remained more or less constant over time, although hooks
with grooves rather than holes for attaching the lines became more
frequent, while the overall length of the hooks decreased
somewhat.
The strength test of the replicas proved no significant difference
in strength between the two raw-materials, moose and wild boar
bone. However, the ultimate loads at rupture were in three cases of
four somewhat higher for the hooks made of wild boar bone. The
fracture areas and surface textures of the replicas were similar to
those of the original incomplete hooks with fresh breaks. The
breakage study of the strength-tested replicas and original incomplete hooks made it possible to distinguish fresh breaks from
dry breaks. The breakage pattern showed that bow fractures were
the most common among fresh breaks. Shank fractures were most
frequent, but were dominated by dry breaks, and therefore more
related to post-depositional processes. The strength test and the
morphology study supported our hypothesis that line fishing for
cod, in deep waters, from boats, some distance from the site, was
the field of application for the majority of the fishhooks from
Ajvide. Hook sizes and cod sizes appear to be related, also suggesting that cod was the main target of the Ajvide hook and line
fishery.
Acknowledgements
Fig. 9. Percentage single fractures (fresh and dry) per chronological level (n ¼ 189).
HF ¼ head fracture, SF ¼ shank fracture, BF ¼ bow fracture, PF ¼ point fracture.
We thank Hans Öberg, Senior Research Engineer at the Department of Solid Mechanics, KTH Royal Institute of Technology in
2822
C. Olson et al. / Journal of Archaeological Science 35 (2008) 2813–2823
Stockholm, who carried out the strength test and documented the
results from this test. Without his kind help and interest in Stone
Age technology, we doubt this test could have taken place. We are
also most grateful to Dr. Inger Österholm, now sadly deceased,
Professor Göran Burenhult and Johan Norderäng at the University
of Gotland for access to the fantastic fishhook assemblage from
Ajvide and generous permission to borrow original fishhooks for
the manufacturing of replicas for this study. We thank Dr. Jan Storå
for critical comments, fruitful discussions and for continuously
commenting on the manuscript. Thanks also to Dr. Sabine Sten at
the University of Gotland and fisherman John Nordberg from Fårö,
Gotland, who made a fishing experiment possible by using a replica
from the Ajvide assemblage for fishing cod (and caught one!). Carina Olson also wishes to acknowledge the support of her senior
supervisor professor Ebba During who was highly involved in the
fishhook study, but sadly passed away before it was completed.
Finally, we thank the Helge Ax:son-Johnson Foundation for financing the manufacture of the replicas and the strength test, the
Berit Wallenberg Foundation, the Royal Gustav Adolf Academy and
the Hildebrand Foundation for financing the study of the Ajvide
fishhook assemblage. KL was supported by National Science
Foundation grant DEB-0238121.
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