Bycatch and strandings programs as ecological indicators for data-limited cetaceans

Abstract

a b s t r a c tAn integrated approach of using strandings and bycatch data may provide an indicator of long-term trends for data-limited cetaceans. Strandings programs can give a faithful representation of the species composition of cetacean assemblages, while standardised bycatch rates can provide a measure of relative abundance. Comparing the two datasets may also facilitate managing impacts by understanding which species, sex or sizes are the most vulnerable to interactions with fisheries gear. Here we apply this approach to two long-term datasets in East Australia, bycatch in the Queensland Shark Control Program (QSCP, 1992(QSCP, -2012 and strandings in the Queensland Marine Wildlife Strandings and Mortality Program (StrandNet, 1996(StrandNet, -2012. Short-beaked common dolphins, Delphinus delphis, were markedly more frequent in bycatch than in the strandings dataset, suggesting that they are more prone to being incidentally caught than other cetacean species in the region. The reverse was true for humpback whales, Megaptera novaeangliae, bottlenose dolphins, Tursiops spp.; and species predominantly found in offshore waters. QSCP bycatch was strongly skewed towards females for short-beaked common dolphins, and towards smaller sizes for Australian humpback dolphins, Sousa sahulensis. Overall, both datasets demonstrated similar seasonality and a similar long-term increase from 1996 until 2008. Analysis on a species-byspecies basis was then used to explore potential explanations for long-term trends, which ranged from a recovering stock (humpback whales) to a shift in habitat use (short-beaked common dolphins).Crown

Understanding Strandings: 25 years of Humpback Whale (Megaptera novaeangliae) Strandings in Queensland, Australia

“…Similar to findings elsewhere (Capella-Alzueta et al, 2001;Holyoake et al, 2012;Moura et al, 2013), calves and juveniles dominated strandings with only 15-20% of the strandings involving adults, and the peak strandings rate occurred late in the austral winter (Meager and Sumpton, 2016). Mother and calf pairs are known to prefer to rest in shallow, sandy bays during the southern migration, which makes them more susceptible to anthropogenic impacts and strandings (Franklin et al, 2011;Holyoake et al, 2012;Meynecke et al, 2013).…”

The impact of environmental factors on marine turtle stranding rates

“…Within StrandNet, the primary cause of death/stranding was identified based on gross examination, photograph and/or necropsy by trained personnel [ 12 , 29 ]. The single cause of stranding identified in StrandNet was based on the summation of information available.…”

Cetacean biodiversity, spatial and temporal trends based on stranding records (1920-2016), Victoria, Australia

“…Effective conservation of cetacean populations requires an understanding of temporal and spatial incidence, species richness and community composition, as well as demographic and life history parameters of populations within a region [1, 2]. Comprehensive data on cetacean species is inherently difficult and expensive to collect [3, 4]; however, strandings (defined in this study as; beach-cast animals, dead or alive [5]) can provide valuable information on species presence and distribution [6, 7], species composition [3, 8], population dynamics [3, 8, 9], stranding type (e.g., single or mass), anthropogenic impacts such as ship strikes and bycatch [4], health of wild populations [10], and diet [11].…”