Temporal stability of the maturation schedule of capelinMallotus villosusin the Barents Sea

Abstract

-Capelin in the Barents Sea are primarily harvested in a terminal fishery that targets maturing individuals. Theory predicts that, in a semelparous population (i.e., one in which reproduction is seasonal, synchronous, and followed by parental mortality), an unselective, terminal fishery (i.e., one in which most of the fish that are not caught will not have a new spawning opportunity) does not generate strong selection for changed age and size at maturation. The probabilistic maturation reaction norm (PMRN) method was applied to test this prediction and to detect possible temporal changes in length at maturation of Barents Sea capelin between 1978 and 2008. Maturation reaction norms suggest that maturation is age-independent in capelin, but that males require a larger size to attain the same maturation probability as females. No temporal trends in length at maturation could be detected, thus confirming the theoretical prediction. Furthermore, none of the candidate environmental variables tested to explain the temporal variability in length at maturation (water temperature and capelin biomass) consistently showed a significant correlation with the PMRN midpoints.

Fisheries-Induced Evolution

“…Many of the negative findings come from short-lived species that naturally experience high mortality and exhibit early maturation (e.g., Norway pout, sardine, and capelin; Baulier et al 2012. Arguably, such species are already adapted to high mortality levels and may therefore have little scope for a further acceleration of their maturation.…”

“…Arguably, such species are already adapted to high mortality levels and may therefore have little scope for a further acceleration of their maturation. Some others come from populations that are selectively harvested at spawning grounds only (Norwegian spring spawning herring; Engelhard & Heino 2004) or are semelparous and subject to terminal harvest (capelin, Pacific salmon; Baulier et al 2012, settings that are known to exert less selection on maturation. A few other negative cases are associated with short time series that may have lacked statistical power.…”

Predator‐prey interactions cause apparent competition between marine zooplankton groups

“…For example, zooplankton or other environmental factors can affect maturation not only through length, as modelled (and empirically supported, Baulier et al 2012), but also through the condition of the capelin (Orlova et al 2010). For example, zooplankton or other environmental factors can affect maturation not only through length, as modelled (and empirically supported, Baulier et al 2012), but also through the condition of the capelin (Orlova et al 2010).…”

“…While our results provide interesting insights into the predator-prey dynamics among zooplankton and capelin, there are some caveats worth mentioning. For example, zooplankton or other environmental factors can affect maturation not only through length, as modelled (and empirically supported, Baulier et al 2012), but also through the condition of the capelin (Orlova et al 2010). Furthermore, even if our model is both age-structured and accounts for some of the spatial structure in the system, there may be processes at other stages or spatial scales that can potentially affect the dynamics of the system.…”

“…Capelin biomass was calculated from the modelled abundanceat-age and length-at-age based on length-weight relationships described in the literature (Monstad 1971, Gjøsaeter 1998. Maturation depends on length with 50% maturity around length L p50 = 14 cm (Gjøsaeter 1998, Baulier et al 2012. Hence, variable fractions of 2-and 3-year-olds contribute to the following year's spawning stock, depending on the mean length of the year-class.…”