A Life History Approach to the Assessment and Management of Deepwater Fisheries in the Northeast Atlantic

Abstract

It has been generally stated that fish exploited by deepwater fisheries cannot sustain high levels of exploitation because of their characteristic slow growth, longevity and low reproductive output. Irish surveys (19932000) allowed for studies of age, growth, fecundity and maturity of several deepwater teleosts and elasmobranchs. These data show that the teleost roundnose grenadier Coryphaenoides rupestris is slow growing and has low fecundity. Other teleosts also displayed rather conservative life-history characteristics. The birdbeak dogfish shark Deania calceus was slower growing than the teleosts and leafscale gulper shark Centrophorus squamosus attained ages of up to 70 years. The implications of these life-history parameters for sustainable exploitation are discussed by way of comparison with continental shelf species from this region. These data allowed for the estimation of the rate of potential population increase that supports the view that deepwater species are more vulnerable to exploitation. Whilst there may be scope for compensatory changes in fecundity such scope is likely to be limited, especially for sharks. Fisheries management plans should consider these differing life-history traits. The very different life history strategies exhibited by shelf and deepwater species suggests that different management systems will be required for deepwater fisheries to those prosecuted on the shelf.

Image-enhanced burnt otoliths, bomb radiocarbon and the growth dynamics of redfish (Sebastes mentella and S. fasciatus) off the eastern coast of Canada

“…By the time it was realised that the species grew extremely slowly and could live to an age of more than 100 years (Smith et al 1995;Andrews et al 2009), the damage had been done and many populations had already been fished almost to the point of collapse. It is possible that roundnose grenadier (Coryphaenoides rupestris) in the north-west Atlantic will never recover from its fishery, in part because of slow growth rates and longevities of 60 years, which are much greater than previously suspected (Clarke et al 2003). Indeed, longevities exceeding 100 years become increasingly frequent as habitat depth increases (Cailliet et al 2001;Roberts 2002), an observation that would have been ridiculed some 30 years ago (Campana 2001).…”

“…It has been recognised only recently that deep-sea fishes tend to be slow growing, long lived and characterised by a late age of sexual maturation, making them particularly sensitive to overfishing and slow to recover from depletion (Clarke et al 2003). Some high-profile examples of serious overfishing have occurred, at least in part, because of overly optimistic impressions of growth and productivity brought on by age underestimation.…”

Assessing the risk of vulnerable species exposure to deepwater trawl fisheries: the case of orange roughyHoplostethus atlanticusto the west of Ireland and Britain

“…In contrast, the deepwater sharks, such as Centroscymnus coelolepis and Centrophorus squamosus, fell into the low productivity category. In addition to their large body sizes and high longevity, their low reproductive potential increases their vulnerability still further (Clarke et al 2003), which was fully reflected in the multispecies PSA output.…”

Sharks, rays and chimaeras: the status of the chondrichthyan fishes

“…Information is generally scarce for all species of deepwater sharks, which have only recently become the subject of regular monitoring, sampling and commercial fisheries that are still unregulated (Clarke et al 2002a(Clarke et al , 2002bCrozier et al 2002;Figueuredo et al 2002). Exploratory surveys have begun to provide preliminary information on their status (unfortunately this is as a result of the introduction of commercial fisheries for these species, so it is too late to provide a baseline for monitoring).…”