Fishing effects in northeast Atlantic shelf seas: patterns in fishing effort, diversity and community structure. II. Trends in fishing effort in the North Sea by UK registered vessels landing in Scotland

128

107

The recent decline in many fish stocks has been accompanied by marked changes in age at maturity. However, there is little information on whether other components of reproductive investment have changed and the relative roles of phenotypic plasticity or genetic selection in such change. This study explored how reproductive investment in cod Gadus morhua from different regions around Scotland has changed between a period of high (1969, 1970) and low (2002, 2003) spawning-stock size. Maturity ogives indicated that inshore North Sea cod now mature at a smaller size and younger age than they did around 1970. The relationship between potential fecundity and size indicated that cod in the inshore region are now more fecund than 30 yr ago. Cod from the inshore region of the North Sea now have a higher fecundity at a given size and age than cod from the offshore region and the west of Scotland. There was no such spatial trend around 1970. Similarly, whilst the relative fecundity of cod in recent times is positively correlated with age, no such relationship was evident in 1969 and 1970. Nutritional influences on maturity and fecundity, particularly liver condition, were also evident from the recent study. However, the temporal and spatial differences in fecundity-size relationships were not consistent with a change in growth conditions, as there has been a significant decrease in body condition in recent times. Our findings regarding the temporal change in reproductive investment in the inshore North Sea region appear consistent with genotypic changes in life-history traits predicted to arise from intense periods of size-selective mortality.

Section: Discussionmentioning

confidence: 78%

Temporal and spatial variation in reproductive investment of Atlantic cod Gadus morhua in the northern North Sea and Scottish west coast

Yoneda

Wright²

2004

128

107

“…Such high levels of mortality may markedly increase the risk of reproductive failure for a cohort (Wright & Trippel 2009). Although there is no information on regional mortality rates, most demersal fishing effort in the northern North Sea was concentrated in the west coastal North Sea until recently (Jennings et al 1999, Greenstreet et al 1999. Consequently, it is highly likely that fishing mortality was historically much higher on the sub-population that has undergone the largest change.…”

Section: Discussionmentioning

confidence: 99%

Reproductive investment in the North Sea haddock: temporal and spatial variation

Wright¹,

Gibb²,

Gibb³

et al. 2011

Maturation and fecundity have been examined since the 1970s in 2 putative sub-populations of North Sea haddock Melanogrammus aeglefinus. Reproductive investment within the western North Sea haddock sub-population significantly increased between the 1970s and 2000s, as was evident from both a decline in maturation probability and an increase in fecundity with size. A decline in maturation probability was also evident in males from the east North Sea, although the length at 50% probability of maturing (Lp50) at the beginning and end of the study period was much higher than in the west North Sea. The changes in reproductive traits could not be explained as a compensatory response, since the trend for increasing reproductive investment was not reversed when the North Sea stock recovered over the past decade. Indeed increased reproductive investment was accompanied by a reduction in somatic growth rate. Temperature immediately prior to secondary gametogenesis could partially explain inter-annual variation in female maturation probability and may have influenced the difference in sub-population trends. However, declines in maturation probability with cohort were still highly significant after accounting for a temperature effect, and differences in potential fecundity could not be explained by changes in somatic condition. Overall, it appears that west North Sea haddock have increased their reproductive effort, following decades of high mortality, consistent with an evolutionary response.

“…These include fishing effects that directly (targeting) and indirectly (bycatch) impact populations, fishing effects that directly and indirectly impact benthic habitats, and climate change. Long-term trawling has permanently altered benthic habitat and prey community for parts of this and other marine ecosystems (Collie et al 1997, Greenstreet et al 1999a,b, Garrison & Link 2000a,b, Kaiser & de Groot 2000, Kaiser et al 2000, Hermsen et al 2003. Perturbations such as trawling may have additional unexpected impacts in the wake of climate change (Anthony et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Stability in the feeding ecology of four demersal fish predators in the US Northeast Shelf Large Marine Ecosystem

Byron¹,

Link²

2010

Evidence of species interactions are generally well understood over broad temporal and spatial scales, particularly for commercially valuable species. Yet species that are not as commercially valuable may nonetheless be ecologically important in stabilizing trophic interactions in large marine ecosystems. We examined the diets for 4 of these demersal fish species: black sea bass Centropristis striata, scup Stenotomus chrysops, Northern searobin Prionotus carolinus, and striped searobin P. evolans. We examined food habits data across size class, season, 5 yr time block, and geographic region to evaluate the major determinants of diet composition. We used multivariate statistics, specifically canonical correspondence analysis, as the primary method to explore diet determinants. Our results showed that the scup and 2 searobin species are primarily benthivorous, whereas black sea bass notably shifts towards piscivory with ontogeny. Our results also showed that the diet of these predators was mainly influenced by size class, region, and (to a lesser extent) season, whereas 5 yr time block did not notably influence diet composition, a surprising observation given the welldocumented changes to benthic habitat in this ecosystem. These results suggest that these species feed opportunistically in proportion to the relative abundance of available prey given the constraints of their morphology, which implies that despite notable impacts to benthic habitat, the prey field for these understudied species has been consistent (within seasonal variation) over the past 3 decades. Stable feeding dynamics such as these may act to enhance resilience in large marine ecosystems.KEY WORDS: Black sea bass · Scup · Northern searobin · Striped searobin · Benthic · Ontogenetic shifts · Northwest Atlantic · Canonical correspondence analysis 406: 239-250, 2010 thought to enhance stability of the food web, which can then enhance the stability and resilience of the entire system (Holling 1973). Predator-prey relationships may differ at different spatial and temporal scales and with varying degrees of disturbance. The scale at which these stabilizing mechanisms take place and the severity of disturbance may determine the extent to which the system can be managed, or at least its resilience for management assumptions, functionally speaking (Auster & Link 2009). Therefore, examining a system and the interactions with that system at the same scale at which it is managed is critical (Sherman 1991(Sherman , 1994(Sherman , 2006. Resale or republication not permitted without written consent of the publisher OPEN PEN ACCESS CCESSMar Ecol Prog SerThe US Northeast Shelf (NES) LME has had an actively managed fishery for more than 3 decades and has experienced a wide range of impacts and disturbances (Fogarty & Murawski 1998, Garrison & Link 2000a,b, Link et al. 2008, Auster & Link 2009). These include fishing effects that directly (targeting) and indirectly (bycatch) impact populations, fishing effects that directly and indirectly impact benth...