Pelagic longlines and albatross in the southern Indian Ocean : interactions of fleet dynamics, climate change, and albatross
Creators: name: Michael, PE
Publisher: name: University Of Tasmania
Year: 2023

description: The greater Southern Ocean is vast, valuable, and vulnerable. Land masses are few and intense atmospheric and oceanographic conditions create a mosaic of logistical challenges for access. The Southern Ocean is home to unique species, including all but three of the world's albatross species and high value tunas targeted by distant-water pelagic longline fleets from multiple flagstates. Exploitation of tunas has contributed to some stocks being over-fished while indirect exploitation, through incidental bycatch, has severely impacted many albatross colonies. The impacts of climate change will further complicate the current interactions within the Southern Ocean, including those between fish, fishers, and albatross. This thesis predicts the potential future for Southern Ocean tuna, fishers, and albatross, focusing on the Indian Ocean sector of the Southern Ocean, with some analyses in the Atlantic sector as well. The first chapter introduces the Southern Ocean, major tuna fisheries, their interactions with albatross and the potential impacts of climate change. It then describes the approach taken in this thesis. As fishers interact with both fish and albatross, the second chapter quantifies the broad-scale patterns in pelagic longline effort across both the Indian and Atlantic sectors of the Southern Ocean. This assessment reveals a strong seasonal cycle in the magnitude and distribution of effort in both sectors, generally in association with changing target species. This shift in target species is associated with both ecological (species moving to different areas) and management (start of the quota year) conditions. The third chapter develops a novel approach to modeling fleet dynamics for distant water pelagic longline effort for Japanese and Taiwanese fleets. These models project the potential impacts of climate change on the distribution of fishing effort. From a range of effort allocation strategies that consider modelled catch per unit effort (CPUE) of four different tuna species, cost, value, and predicted variability in CPUE in each fished area, the distribution of effort in both fleets was most similar to preferentially allocating effort into areas of low predicted variability. Using environmental parameters projecting climate change in our tuna distribution models, the models forecast an average decrease in CPUE, an increase in the average predicted variability of CPUE, and decrease in effort, related to the fishing strategy identified above; fishing in areas of low predicted variability. The fourth chapter assesses the population dynamics of black-browed albatross (Thalassarche melanophris) breeding on Kerguelen Island, in the central western portion of the study area. This assessment uses an integrated population model structured by sex, age-class, breeding stage, and reproductive history and operates on a monthly, 5vÄv¿ ‚àöv= 5vÄv¿ temporal and spatial scale. We quantify the bycatch of each super-fleet (fleets grouped by gear-type and reported bycatch rates) and the impact of environmental conditions on the albatross population. These analyses indicate that high bycatch in the 1990s- early 2000's decreased the population, with bycatch attributed to illegal, unreported and unregulated (IUU) demersal and non-Japanese pelagic longline effort, although the model's ability to differentiate bycatches between pelagic super-fleets is weak. In line with other studies, warmer SSTs during the incubation period favors higher productivity. In the final research chapter, the models described above (Ch. 3 and 4) are combined to project the synergistic impacts of climate change on albatross and fleet dynamics. Reduced effort by the Taiwanese and Japanese fleets had very little impact on the population, as bycatch by pelagic longline fleets was projected to be virtually absent even with higher levels of effort. The impact of warming SST during the incubation period increased chick survival. However, the associated increase in juvenile and immature albatross in the following years results in a density-dependent decrease in juvenile survival to age five, ultimately reducing the total number of breeding pairs in the population relative to a projection assuming no change in SST. This work presents one of the first examples of research combining fleet dynamics with albatross population dynamics to quantify the potential impacts of climate change. The patterns identified in the broad-scale distribution of fishing effort (Ch. 2) informed the development of the fleet dynamics model (Ch. 3). After a thorough analysis of the drivers of black-browed albatross population dynamics, including the environment and bycatch of multiple fleets (Ch. 4), these projections were combined (Ch. 5).This approach demonstrates the utility of fleet dynamics models and underscores the flexibility of integrated population models when assessing how changes in multiple factors (e.g. environmental parameters, bycatch) can impact a given population in the future. These types of models can assist conservation and fisheries managers make important decisions regarding mitigation of both bycatch and the environmental impacts of climate change.