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doi: 10.1006/jmsc.1996.0096pmid: N/A
The food and feeding of Flemish Cap cod are described for 5 years based on 3921 stomachs collected in the fishing grounds off the Flemish Cap, Newfoundland in summer 1989–1993. Feeding intensity was high but the prey spectrum was narrow in all years with hyperiids and redfish (Sebastes sp.) predominating. Squid and poly-chaetes had a high inter-annual variability. Juvenile cod diet was dominated by crustaceans, mainly hyperiids, and polychaetes, while in adult cod diet the most important prey were fish, mainly redfish. The maximum size of redfish eaten increased with cod size, but prey–predator size relationships showed weak correlation. Cannibalism increased in 1991 (mainly upon 1-year-olds), coinciding with the appearance of a large year class in 1990. In the years 1992 and 1993, a change in the diet was observed involving an increase of hyperiids in the adult cod diet and a decline of redfish.
Fjøsne, Karen; Gjøsæter, Jakob
doi: 10.1006/jmsc.1996.0097pmid: N/A
0-group cod (Gadus morhua L.), 0-group whiting (Merlangius merlangus L.), goldsinny wrasse (Ctenolabrus rupestris L.), and black goby (Gobius niger L.) were caught near Arendal in August and October 1991. Dietary composition showed that 0-group cod mainly ate calanoid copepods, gammarids, shrimps or prawns, crabs, and fish. They were generalists with a wide feeding niche. Mostly active benthic, hyperbenthic, and pelagic prey were ingested. 0-group whiting mostly ate calanoid copepods, hyperids, crabs, appendicularians, and fish. They were more specialised feeders than 0-group cod. On some occasions, whiting ate large amounts of megalopas and calanoid copepods. Prey were active benthic, hyperbenthic, or pelagic and consisted of more pelagic prey and fish than that of any of the other fish species. Goldsinny wrasse were generalists and mostly ate bryozoans, gastropods, bivalves, caprellids, gammarids, shrimps or prawns, and crabs. Prey were active, slow moving, or sedentary, and mostly benthic or hyperbenthic. Black goby mostly ate gammarids, crabs, and fish, but many of them also ate gastropods, bivalves, shrimps or prawns, insects, and poly-chaetes. They were also generalists with a wider feeding niche than 0-group cod and 0-group whiting. Black goby ate active, slow moving, or sedentary prey, mostly benthic or hyperbenthic.Dietary composition differed significantly between locations in each period and between periods in each location for all species (except black goby).The diets of 0-group cod and 0-group whiting were more similar compared to the diets of the other fish, indicating potential food competition only between these two species. Both ate many fish, but also, on some occasions, many megalopas and the copepod species Calanus finmarchicus. Differences in behaviour may, however, reduce competition.
doi: 10.1006/jmsc.1996.0098pmid: N/A
A biologically sensible model for cod recruitment in the central Baltic is proposed. The model takes into account, in a simple way, (1) the spawning stock size of cod, (2) the annual spawning conditions in terms of salinity and oxygen content, and (3) the predation on cod eggs by sprat. The parameters are estimated using regression analysis methods. All three factors are shown to be statistically significant, although sprat predation is the least clear effect. The model residuals are not correlated (no auto-correlation). The model is successfully evaluated against independent data. According to the model, cod recruitment at age 0 is proportional to the spawning stock biomass (SSB) for realistic ranges of SSB, for a given set of spawning condition and sprat predation. It is further shown that it is important to use recruitment data from an MSVPA, where cod cannibalism is included, in stock recruitment analysis of central Baltic cod.
McClatchie, Sam; Alsop, Jon; Coombs, Roger F.
doi: 10.1006/jmsc.1996.0099pmid: N/A
There are many measurements of dorsal aspect target strength of fish, but relatively few studies compare estimation methods or attempt to combine data from different studies into general relations between fish size, acoustic frequency and target strength (or acoustic cross-section). We edited and updated earlier summary regressions relating fish size, acoustic frequency and acoustic cross-section. Experimental measurements on marine fish were separated into swimbladder and non-swimbladder species, model results compared with experimental data, target strengths of marine, and freshwater fish were contrasted, and previous and new target strengths of commercial New Zealand fish species were placed in the context of the new regressions. Analysis of variance was used to show significant effects of species, freshwater vs. marine, swimbladder vs. non-swimbladder fish, model vs. experimental, and dead vs. alive fish on the relationship between maximum dorsal aspect target strength and fish length. For experimental results on gadoids we found significant species and live vs. dead (or stunned) fish effects on the target strength to length relationship. The quadratic dependence of target strength on fish length was also tested and found to be the exception rather than the rule. Existing pitch tilt angle data was compiled and a normal distribution with standard deviation of at least 15° was required to describe most distributions.
doi: 10.1006/jmsc.1996.0100pmid: N/A
Growth rates, hatch0date distributions and seasonal changes in energy content of larval and juvenile herring (Clupea harengus), the major Baltic Sea zooplanktivore, were studied in a coastal area. The first microstructure (ring) shown in the otoliths (sagittae) was formed at the end of the yolk0sac stage. The following rings occurred regularly and showed a pattern corresponding to daily growth rings, as described in the literature, and we used these rings to age the fish. The average growth rate was estimated at 0.37 mm d−1 and 0.58 mm d−1 for larval and metamorphosed herring, respectively. The overall growth for all young stages could be described with a fourth order polynomial relationship between length and age. Estimated hatching dates were distributed between March and June. This is earlier than normally assumed for the northern Baltic Sea and was probably caused by an early and warm spring in 1993. Our data indicate the highest survival for herring spawned from end of April to the middle of May. In terms of seasonal and yearly fluctuations in body composition, there was an increase in energy content from 2200 to 2800 J g−1 wet weight and 2900 to 4800 J g−1 wet weight for larval and metamorphosed herring, respectively, with nearly constant energy content during metamorphosis.
González, Angel F.; Castro, Bernardino G.; Guerra, Angel
doi: 10.1006/jmsc.1996.0101pmid: N/A
Age and growth of Illex coindetii in the fishery northwest of Spain were estimated from statolith growth increments. 341 statoliths were examined (170 males, 171 females) from individuals of 48–379 mm mantle length (ML). The maximum size of squids was 279 mm ML for males and 379 mm ML for females. Weight-at-length of mature males was greater than that of immature males and mature and immature females. Lifespan was estimated at 13 months for males and 15 months for females. Recruitment to the fishery occurred approximately at three months of age. Mantle length instantaneous relative growth rates were 0.72 mm d−1 for males and 0.84 mm d−1 for females. Weight growth rate was 2.22 g d−1 for males and 3.66 g d−1 for females. Maturity stages, however, influenced increase in weight in both sexes, such that weight-at-age was greater for mature than for immature individuals. The age at which individuals mature is variable, ranging from 140 to 271 d in males and between 183 and 285 in females. Growth rates in both sexes were dependent on the season of hatching. Squids hatched in winter attained larger sizes for the same age than squids in other seasons. These seasonal differences in growth were only evident after squids had reached 8 months of age. Reading daily increments in statoliths seems to be a reliable technique for studying the age and growth of Illex coindetii.
Erzini, Karim; Gonçalves, Jorge M. S.; Bentes, Luis; Lino, Pedro G.; Cruz, João
doi: 10.1006/jmsc.1996.0102pmid: N/A
The species and size selectivity of long-lines using small hooks were studied off the south coast of Portugal using “Mustad” brand round bent, flatted sea hooks (Quality 2316 DT) numbers 15, 13, and 11 baited with razor shell clam (Ensis siliqua). Hook numbers 13 and 11 are 49 and 109% larger respectively than number 15 hooks in terms of overall size (maximum width × maximum length). A total of 39 900 hooks were fished in 45 sets and 35 species of fish and cephalopods were caught. As a group, 13 species of sea breams (Sparidae) dominated the catch by numbers (58%) and weight (73%). Six species of sea breams, along with the greater weever fish (Trachinus draco) accounted for 81% of the total catch by weight, with the common or white sea bream (Diplodus sargus) being the most important (29%). Catch size distributions by hook size were, in general, highly overlapped for all species and hook size had little apparent effect on minimum size at capture. All hooks caught a wide range of sizes per species, but the catch rate (number of fish per 100 hooks) was significantly lower for the largest hook. Except for the black sea bream (Spondyliosoma cantharus), capture of illegally sized or immature fish was minimal. Small increases in average size with hook size were evident for four species: Diplodus sargus, D. vulgaris, Lithognathus mormyrus and Serranus cabrilla. No differences in size selectivity were detected for Boops boops, D. annularis, Spondyliosoma cantharus and Trachinus draco. A skew-normal model adequately described differences in size selectivity in five of six species.
doi: 10.1006/jmsc.1996.0103pmid: N/A
Research vessel survey data from the northern Grand Bank and southern Scotian Shelf/Bay of Fundy were analysed for evidence of the occurrence of shoals of Atlantic cod (Gadus morhua) with unequal sex ratios during the spawning season. Cod were found to form both male dominated and female dominated shoals during spawning. In both areas, female dominated shoals were found in significantly deeper waters. A higher proportion of both males and females were in spawning condition in the male dominated fishing sets and a higher proportion of females had completed spawning in the female dominated fishing sets. Males may arrive at the spawning area first, with females moving into the area when ready to spawn and then returning to deeper, warmer water once they have completed spawning.
Suthers, Iain M.; Sundby, Svein
doi: 10.1006/jmsc.1996.0104pmid: N/A
Size-at-age of pelagic juvenile cod from the north-east Atlantic off northern Norway was approximately twice that of cod from the north-west Atlantic, off south-western Nova Scotia, Canada. Arcto-Norwegian cod (AN, 17–48 mm standard length, SL, 34–90 d post-hatch), were sampled in July 1988 with a capelin pelagic trawl, while south-west Nova cod (NAFO region 4X, 7–32 mm SL and 32–105 d post-hatch) were sampled in May–June 1985–1986 with a Tucker trawl. Growth over the previous 14 d, back-calculated from otolith daily growth increments was 0.71 mm d−1 and 0.33 mm d−1 for AN and 4X cod respectively. Within and between stocks, water temperature and zooplankton biomass were significantly correlated with the 14 d index (linear model, r2=0.42), but an ANCOVA model comparing the AN and 4X regions was highly significant (r2=0.71), indicating additional factors. Gear selection was not found to be responsible. While genetic factors could produce this result, there is 48% more time during May–July for visual feeding north of the 71°N latitude off Norway compared with 43°N off eastern Canada, using the light intensity threshold for larval cod feeding. Our hypothesis of light-limited feeding opportunity is consistent with a size- and temperature-dependent consumption model, and with aquaculture methods, as well as the necessity for fast growth in the short northern summer for over-winter survival.
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