Implications of recent increases in catches on the dynamics of Northwest Atlantic spiny dogfish (Squalus acanthias)

Rago, Paul J.; Sosebee, Katherine A.; Brodziak, Jon K. T.; Murawski, Steven A.; Anderson, Emory D.

doi:10.1016/s0165-7836(98)00181-7

Cited by 61 publications

(46 citation statements)

References 9 publications

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“…Our comparison of the catch size frequency, distributed over both experiments, revealed a displacement of the distribution towards smaller sizes over time. Similar changes have been observed in the size composition of exploited populations of Squalus acanthias [30], sharks, rays and chimaerae [31], Ammodytes marinus [32], Sander lucioperca [33] and different species from the communities of coral reefs [34]. Variations in fish population size frequency distributions have been identified as possible indicators of the impact of fishing [35].…”

Section: Discussionsupporting

confidence: 52%

Deep water longline selectivity for black spot seabream (Pagellus bogaraveo) in the Strait of Gibraltar

et al. 2009

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Species and size selectivity of the deep water longline traditionally used in commercial fishing of the black spot seabream (Pagellus bogaraveo) were studied in the Strait of Gibraltar with four sizes of hooks. Black spot seabream contributed up to 88% of the catch by number. Catch and by-catch rates differed for the different hooks and fishing trials. Significant differences in average fish length between all hooks, except in one case, were found. The comparison of two experimental fishing trials within 4 years indicates a displacement towards smaller sizes in the size frequency distributions. The results of this study show that the fishing gear can be size selective depending on hook size. The fitted selectivity models for each experiments were very different despite having two hooks in common. This is probably due to the very different catch size distributions in the two periods, which suggests that the population size structure changed significantly between

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Section: Discussionsupporting

confidence: 52%

Deep water longline selectivity for black spot seabream (Pagellus bogaraveo) in the Strait of Gibraltar

et al. 2009

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“…The last study on reproduction of spiny dogfish in the Northwest Atlantic was conducted in the late-1980s (Silva, 1993). At that time, the biomass of the stock was increasing from low levels in the 1970s (NEFSC, 1998;Rago et al, 1998). A stock assessment conducted in 1997 determined that the biomass of large females (>80 cm) was 50% of the 1989 peak (NEFSC, 1998).…”

Section: Introductionmentioning

confidence: 99%

Are Density-dependent Effects on Elasmobranch Maturity Possible?

Sosebee¹

2005

J. Northw. Atl. Fish. Sci.

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Fecundity and size at first maturity of elasmobranchs are believed to be limited by body size, making density-dependent effects on these life history traits unlikely. To examine the potential for density-dependent effects on size at first maturity, female spiny dogfish (Squalus acanthias) off the northeast coast of the United States were examined to determine both the presence of free embryos, fertilized eggs, or ovarian eggs, and the number of free embryos in each female in relation to maternal body size during 1998-2002. Severe biomass declines of the adult female portion of the population preceded and continued throughout the study period. Since the period of high abundance in the late1980s, size at first maturity has declined from 75 cm to 66 cm and the median size at maturity (L 50 ) has declined from 85 cm to 79 cm; however, the relationship between number of free embryos and maternal length has not changed.

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“…Each group contains commercial and non-commercial fish species. Since Squalus acanthias (dogfish) is partially migratory (Campana et al 2007), we weighted its biomass by 0.5 to reflect its annual residency (Rago et al 1998). Following Shackell & Frank (2007), six finfish functional groups were denoted: small (less than 46 cm), medium (46 cm or more and less than 80 cm) and large (80 cm or more) benthivores (primarily consumers of bottom dwellers), piscivores (primarily consumers of fish, i.e.…”

mentioning

confidence: 99%

Decline in top predator body size and changing climate alter trophic structure in an oceanic ecosystem

et al. 2009

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Globally, overfishing large-bodied groundfish populations has resulted in substantial increases in their prey populations. Where it has been examined, the effects of overfishing have cascaded down the food chain. In an intensively fished area on the western Scotian Shelf, Northwest Atlantic, the biomass of prey species increased exponentially (doubling time of 11 years) even though the aggregate biomass of their predators remained stable over 38 years. Concomitant reductions in herbivorous zooplankton and increases in phytoplankton were also evident. This anomalous trophic pattern led us to examine how declines in predator body size (approx. 60% in body mass since the early 1970s) and climatic regime influenced lower trophic levels. The increase in prey biomass was associated primarily with declines in predator body size and secondarily to an increase in stratification. Sea surface temperature and predator biomass had no influence. A regression model explained 65 per cent of prey biomass variability. Trait-mediated effects, namely a reduction in predator size, resulted in a weakening of top predation pressure. Increased stratification may have enhanced growing conditions for prey fish. Size-selective harvesting under changing climatic conditions initiated a trophic restructuring of the food chain, the effects of which may have influenced three trophic levels.

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Implications of recent increases in catches on the dynamics of Northwest Atlantic spiny dogfish (Squalus acanthias)

Cited by 61 publications

References 9 publications

Deep water longline selectivity for black spot seabream (Pagellus bogaraveo) in the Strait of Gibraltar

Deep water longline selectivity for black spot seabream (Pagellus bogaraveo) in the Strait of Gibraltar

Are Density-dependent Effects on Elasmobranch Maturity Possible?

Decline in top predator body size and changing climate alter trophic structure in an oceanic ecosystem

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