Implications of climate change for the management of North Sea cod (Gadus morhua)

Abstract

Kell, L. T., Pilling, G. M., and O'Brien, C. M. 2005. Implications of climate change for the management of North Sea cod (Gadus morhua). e ICES Journal of Marine Science, 62: 1483e1491.Robustness of both short-term stock biomass recovery and longer-term sustainable management strategies to different plausible climatic change scenarios were evaluated for North Sea cod (Gadus morhua), where climate was assumed to impact growth and recruitment. In the short term, climate change had little effect on stock recovery, which depends instead upon reducing fishing effort to allow existing year classes to survive to maturity. In the longer term, climate change has greater effects on stock status, but higher yields and biomass can be expected if fishing mortality is reduced. Incorporating environmental covariates in stock assessment predictions will not achieve sustainable resource use. The implications of climate change for biological reference points depend upon the mechanism through which temperature acts on recruitment, i.e. on juvenile survival or carrying capacity. It is not possible to distinguish between these processes with stock assessment data sets alone. However, this study indicates that reference points based on fishing mortality appear more robust to uncertainty than those based on biomass. Ideally, simpler management procedures are required that meet pre-agreed management objectives and are robust to uncertainty about the true dynamics.Crown

Changes in size at maturity of European hake Atlantic populations in relation with stock structure and environmental regimes

“…5d). Impact of fishing mortality on size at maturity has been reported in other species such as cod from Irish and North Sea (Armstrong et al, 2004;Kell et al, 2005), however for Greenland cod no relationship was found between fishing intensity and length at age (Rätz and Lloret, 2005). Fishing activity usually removes larger individuals altering age and length composition of stocks that may result in selection of earlier maturing individuals (Olsen et al, 2004).…”

“…Rose (2005) suggests that small pelagics respond quickly and strongly to climate changes because of their physiological limits and fast potential growth. Moreover, temperature may influence the fish maturation process indirectly through alterations of ecosystem composition, resource availability or hydrographic conditions (Kell et al, 2005;Orlova et al, 2005;Rätz and Lloret, 2005;Rose, 2005). The upwelling process causes a rise of cold deep water rich in nutrients (Wooster et al, 1976;Fraga, 1981) during summer.…”

“…If it continues for long time it can cause the loss of genetic components (Shelton and Healey, 1999), although genetic changes can be explained by other factors such as, genetic flow between close stocks or selective natural predation (Chouinard et al, 2005). In general, is postulated that fishing pressure may modulate fish stock dynamics over shorttime scales while climatic change would have long-time scale effects (Kell et al, 2005;Poulard and Blanchard, 2005;Rose, 2005).…”

Socio-economic Impacts—Fisheries

“…However, scenarios with higher rates of temperature increase resulted in faster rates of decline. In a re-analysis by Kell et al (2005), the authors modelled the effect of introducing a 'cod recovery plan' (as being implemented by the European Commission), under which catches were set each year so that stock biomass increased by 30 % annually until the cod stock had recovered to around 150,000 tonnes. The length of time needed for the cod stock to recover was not greatly affected by the particular climate scenario chosen (and was generally around five to six years), although overall productivity was affected and spawning stock biomass (SSB) once 'recovered' was projected to be considerably less than would have been the case assuming no temperature increase (251,035 tonnes compared to 286,689 tonnes in 2015).…”

Emerging Adaptation Approaches for Climate-Ready Fisheries Management

“…For North Sea cod, for example, an evaluation of management strategies suggested that reduced fishing mortality is one of the most important steps toward rebuilding this overfished stock in both the short and long term, even under a changing climate (Kell et al, 2005). Approaches to reduce mortality could include quotas, effort and gear restrictions, and technical measures to reduce bycatch of juveniles in multispecies fisheries.…”