Biocomplexity and fisheries sustainability

Abstract

A classic example of a sustainable fishery is that targeting sockeye salmon in Bristol Bay, Alaska, where record catches have occurred during the last 20 years. The stock complex is an amalgamation of several hundred discrete spawning populations. Structured within lake systems, individual populations display diverse life history characteristics and local adaptations to the variation in spawning and rearing habitats. This biocomplexity has enabled the aggregate of populations to sustain its productivity despite major changes in climatic conditions affecting the freshwater and marine environments during the last century. Different geographic and life history components that were minor producers during one climatic regime have dominated during others, emphasizing that the biocomplexity of fish stocks is critical for maintaining their resilience to environmental change.climate change ͉ resilience ͉ Pacific salmon ͉ endangered species ͉ biodiversity A t a time of growing concern about the sustainability of many of the world's fisheries, several stand out as providing long-term sustainable yield. Among the most prominent successes are the fisheries for sockeye salmon in Bristol Bay, Alaska (Fig. 1), that have seen record returns and catches in the last two decades. This success is due in part to several factors including (i) favorable ocean conditions in recent decades, (ii) a single, accountable management agency, and (iii) a well established program of limited entry to the fishery. However, the biocomplexity of the stock structure has also played an critical role in providing stability and sustainability. Here we provide evidence for the effects of biocomplexity on sustainability and emphasize that conserving biocomplexity within fish stocks is important for maintaining their resilience to future environmental change. The Biodiversity Of Bristol Bay SockeyeHoming of Pacific salmon (Oncorhynchus spp.) to their natal sites results in reproductive isolation of populations, allowing natural selection to operate on heritable phenotypic traits, and the result is a wealth of distinct, locally adapted populations (1, 2). Sockeye salmon (Oncorhynchus nerka), for example, display a wide variety of life history types, each associated predictably with certain breeding and rearing habitats (3). The diversity of phenotypes thus reflects the adaptation of populations to the diversity of suitable habitats. Spawning by salmonid fishes generally takes place in lotic habitats, and Bristol Bay sockeye salmon spawn in streams and rivers ranging from 10 cm to several meters deep, and in substrate ranging from small gravel to cobble (4, 5). Some creeks have spring-fed ponds with much finer substrate and deeper, slowly flowing water, and these too are used for spawning. Sockeye also spawn in groundwater-fed beaches at the outwash areas of rivers and along hillsides with substantial groundwater inputs. In these habitats, sockeye may spawn from the shoreline to depths of several meters. Finally, sockeye may also spawn on the rocky beaches o...

Population assignment and local adaptation along an isolation‐by‐distance gradient in Pacific cod (Gadus macrocephalus)

“…When management units and associated harvest quotas are not based on realized stock structure, the spatial allocation of fishing may not be proportionate to stock biomass and could result in localized overfishing, particularly if two or more stocks are managed as one (Spies & Punt, 2015). Moreover, disproportionate exploitation of certain stocks may have the potential to destabilize the adaptive resilience of the stock complex as a whole (Hilborn, Quinn, Schindler, & Rogers, 2003). …”

Ecosystem-based fisheries management requires a change to the selective fishing philosophy

“…It is not uncommon that some stocks of a species suffer higher fishing mortality than others (25)(26)(27). This may arise because some stocks are easier to access (e.g., closer to ports).…”

The stochastic nature of larval connectivity among nearshore marine populations

“…Thus, recruitment variability will be inherently unpredictable even in the absence of the sources of spatial and temporal variability that have been commonly studied (6)(7)(8). Connectivity among nearshore populations on annual time scales will not be well modeled by using mean field approaches such as advection/diffusion models, which will make the management of nearshore fisheries difficult (28).…”

“…Stochasticity caused by climate variations has long been known to influence the dynamics of ocean ecosystems and the fisheries they support (6). Climate variation affects rates of fecundity and recruitment by altering water temperature, coastal circulation patterns, or the availability of spawning grounds (7,8); such effects can be understood and, given sufficient data, may be predictable. Here, we introduce a mechanism that generates stochasticity in spatial and temporal patterns of larval transport on annual time scales.…”