Evidence of stability in a chondrichthyan population: case study of the spotted ratfish Hydrolagus colliei (Chondrichthyes: Chimaeridae)

Abstract

Results presented here provide evidence of an exception to the generalization that all chondrichthyan populations are especially vulnerable to exploitation to the extent that they remain at low abundance for a protracted or indefinite duration even after exploitation rates are reduced. Delta log-normal generalized linear models (GLM) and cluster analysis of fishery-independent catch-per-unit-effort (CPUE) data from 1977 to 2006 indicated the presence of at least two distinct stocks of spotted ratfish Hydrolagus colliei off the U.S. West Coast. CPUE of the continental slope and northern continental shelf and upper slope populations did not vary between 1977 and 1995 and increased from 1995 to 2006. On the basis of the timing of these changes, it is likely that both fishing and climate influenced these trends. Sex and size-specific differences in bathymetric distribution, along with the identification of nursery sites, indicate that fishery by-catch could have a significant effect on population growth. These aggregative behaviours, combined with low fecundity, indicate that H. colliei may be vulnerable to irreversible population depletion by fisheries mortality. Temporal abundance trends indicated, however, that their population size has increased significantly within the last decade, a demonstration of population stability. A literature review indicated that there is also evidence for population stability in other chondrichthyans. The paradigm that all chondrichthyan populations fail to rebuild in response to exploitation, therefore, may not be as broadly applicable as previously thought. Thus, it is not necessarily sufficient to make generalizations regarding the vulnerability of chondrichthyans across higher taxonomic scales.

Standardized catch rate of cockfish, Callorhinchus callorynchus, in a bottom trawl fishery of Patagonia: Is it possible its use as a predictor of abundance trend?

“…This model registered the lowest AIC value, presented a good fit of the observed data and explained a 23.5% of the total variability (Table 2). This model selection agrees with other studies of chondrichthyans that are captured as bycatch which used the same error distribution for the positive data set (AIRES et al, 2008;MINISTRY FOR PRIMARY INDUSTRIES OF NEW ZEALAND, 2011;BRACCINI et al, 2011;BARNETT et al 2012;CARLSON et al, 2012). Generally, the models used to standardize the CPUE explained a low percentage of the total variability of the data set.…”

“…However, chondrichthyan species and their populations have different degrees of vulnerability due to their different spatial distribution during different ontogenetic stages, the current commercial interest and the particular characteristics of each fishery. In this sense, stability of chondrichthyan populations that are commercially harvested has been documented in some occasions (WALKER, 1998;MINISTRY FOR PRIMARY INDUSTRIES OF NEW ZEALAND, 2011;BARNETT et al, 2012;CARLSON et al, 2012).…”

“…Therefore, standardization of CPUE considering the effect of these factors and the particular dynamic of each fishery and each species (PUNT et al, 2000;MAUNDER et al, 2006;BRACCINI et al, 2011) is necessary to construct reliable abundance indices (HILBORN andWALTERS, 1992, MAUNDER and. The studies about the abundance trends of chondrichthyans that are caught as bycatch and the factors that influence their catch rate have been increased worldwide both in multispecies and monospecies fisheries (PUNT et al 2000;SIMPFENDORFER et al, 2002;BAUM et al, 2003;AIRES da SILVA et al, 2008;BAUM and BLANCHARD, 2010;CARVALHO et al, 2010;BRACCINI et al, 2011;BARNETT et al, 2012;CARLSON et al, 2012;BROMHEAD et al, 2012, TRAVASSSOS TOLLOTTI et al, 2013.…”

“…Chimaeroids (subclass Holocephali), are a group of chondrichthyan that include species caught as bycatch in several worldwide fisheries whose target species are bony fishes (DI GIÁCOMO and PERIER, 1991;MOURA et al, 2004;MINISTRY FOR PRIMARY INDUSTRIES OF NEW ZEALAND, 2011;BARNETT et al, 2012). Particularly, the species of the genus Callorhinchus are captured and commercially exploited in all their distribution range in the south hemisphere: the elephant fish C. milii in New Zealand (FRANCIS, 1998) and Australia (BRACCINI et al, 2011), the St Joseph C. capensis in South Africa (FREER and GRIFFITHS, 1993) and the cockfish C. callorynchus in Argentina (DI GIÁCOMO and PERIER, 1991) and Chile (ALARCÓN et al, 2011).…”

First record of the chimaera Neoharriota carri (Bullis and Carpenter 1966) in the Caribbean of Guatemala

“…Globally, Chimaeroids are captured incidentally in commercial, recreational and artisanal fisheries (Barnett et al 2012). Despite captures, few data exist regarding their population status; the International Union for Conservation of Nature lists 16 out of 35 chimaera species as data deficient (IUCN 2011).…”