Eleven rajid species are taken around the Falkland Islands, with four species, Bathyraja griseocauda, Bathyraja albomaculata, Bathyraja brachyurops, and Raja flavirostris dominating commercial catches and generally occurring together. Catch limits for individual species are not used in management because species are not separated in the catch or reported separately. The catch per unit effort for the mixed rajid assemblage was standardised using generalised linear modelling techniques, and two production models were used to estimate stock size and sustainable yield. Maximum likelihood methods were used to demonstrate that there are two distinct rajid communities, one to the north and one to the south of the Falkland Islands, which have different sustainable yields. Changes in species composition over the 10-year course of the fishery confirm theoretical expectations that the larger, later-maturing B. griseocauda is being replaced in catches by the smaller, earlier-maturing B. albomaculata and B. brachyurops. These changes in composition were evident after only 6 years of directed fishing. The current fishery to the north of the Falkland Islands appears to be stable at an annual catch of about 3000 t, which is between 6.5 and 7.6% of the estimated pre-exploitation biomass.
The sex of Addie penguins, Pygoscelis adeliae, may be determined by cloacal examination during the early part of the breeding season. Later in the season it becomes increasingly difficult to determine the sex of penguins by this method as the structures used for identification regress. Discriminant analysis of morphometric characters has been suggested as an alternative. This technique was examined for breeding birds of known sex near Mawson Station, Antarctica. The sex of 89% of breeding birds could be correctly determined by comparing the discriminant score D = 0.582 Bl + 1.118 Bd + 0.219Fw, where Bl is bill length, Bd is bill depth and Fw is flipper width, with a mean discriminant score (MDS) of 55.39. In all, the sexes of 87% were correctly determined by means of length and depth only (D=0.601Bl+ 1.154Bd, MDS=44.96). The sex of juvenile birds could not be determined. Determination of sex by discriminant analysis is shown to give acceptable estimates of morphometric characters divided by sex where only the mean and variance of these variables but not the sexual identity of individual birds is required. Where absolute accuracy in sex determination is required, 80% of the birds in our samples would have to be discarded to be 90% confident of the sex of the remainder.
Abstract:In this paper we review evidence for, and anticipated consequences of, climate change in Antarctic marine communities, examining the potential impacts on invertebrates and vertebrates alike and exploring plausible outcomes for species, with examples principally from the Antarctic literature. We suggest that industries with the greatest potential to aggravate climate change impacts on marine communities are marine capture fisheries. In the Southern Ocean, harvesting is governed under the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR). CCAMLR espouses an ecological management framework and so has the capacity to mitigate harvesting impacts such that they do not worsen impacts from climate change. We discuss some of the implications of climate change and advocate that CCAMLR address certain key issues if it is to fulfil its international obligations. It will be essential for CCAMLR to determine relative risks (uncertainties), impacts and timescales, of various processes consequent on climate change. Such risk assessments should be feasible with current knowledge and should provide a focus for future work. We believe it will be important to prioritize issues that reduce impacts and uncertainties by the greatest degree, and propose that future plans should involve shared responsibility (e.g. with SCAR etc.) for each of the risks described.
A multispecies commercial fishery for rajids has been managed in Falkland Islands waters since 1987. In the absence of detailed biological knowledge and catch-at-age data, management policies currently consider a single assemblage rather than individual species. Simple production models with aggregated catch and effort data are used to estimate sustainable levels of exploitation. Biological data, now available from recent research surveys and an ongoing observer program, provide an opportunity to examine the potential impact of the rajid fishery at a species level. This in turn will help determine whether current management policies are still appropriate. An updated assessment of the northern ray population indicates that the assemblage has been surprisingly robust to fluctuations in fishing pressure. A spatial analysis of the relative abundance of animals showed no evidence of local depletions in biomass. At a species level, a declining trend in the relative abundance of three species (Bathyraja griseocauda, B. multispinus, and an undescribed Bathyraja sp. 3) was found at the same time as an increase in two Rajid species (R. doellojuradoi and R. flavirostris). A preliminary analysis of the distribution and movements of R. flavirostris, coupled with length frequency and maturity data, suggest that this species has a broad distribution, which, unlike B. griseocauda, may not form a resident population within Falkland Island waters. While no loss of diversity has been reported, closure of the once heavily exploited area to the south of the Islands provides at least one refuge for species such as B. griseocauda.
Southern blue whiting Micromesistius australis occurs around the southern coasts of South America and has been known to undertake summer feeding migrations to the Antarctic Peninsula and South Orkney Islands. The largest stock spawns to the southwest of the Falkland Islands and has been the subject of a major fishery on the Patagonian Shelf since 1978. Fish are infected with cysts of the Myxosporean parasite Kudoa alliaria which make the flesh commercially unattractive for fillets. A 10 yr study initiated in 1989 established that prevalence of the parasite is over 80% for fish older than 1 yr, and that average infection intensities are about 14 cysts per fish. We constructed a combined generalised linear/generalised additive model (GLM/GAM) of parasite abundance in M. australis. The combination of up to 30 ages and 8 yr of data spanning 10 yr allowed us to investigate rates of parasitism in 33 individual cohorts. Strong age and cohort effects in the model implied that the fish acquire parasites in their first 1 to 1 1 / 2 yr of life and that parasite abundance is set at these ages for the lifetime of the cohort. Several cohorts have statistically significantly lower parasite abundance than the majority, and these instances are roughly coincident with the 7 yr periodicity of seaice and sea surface temperature (SST) fluctuations in the Drake Passage. There are significant correlations between SST in the Drake Passage, the duration of sea-ice around Signy Island (South Orkney Islands) with a 1 yr time lag and parasite abundance in a cohort. We hypothesise that these correlations represent changes in the distribution and density of adult M. australis in warm and cold years, which thereby influences the density of the parasite field that juvenile fish encounter.
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