On the ecology of rorqual whales (Balaenopteridae) in Irish waters using intrinsic markers

Abstract

Despite repeated calls for an ecosystem-based approach to the management of marine resources, little information exists on the ecosystem role and requirements of top predators such as baleen whales in Irish waters. Considering that they are long-lived and highly migratory, baleen whales such as rorquals (Family Balaenopteridae] are potentially useful bio-monitors of anthropogenic environmental change. However, their use as environmental indicators is precluded by an insufficient understanding of their basic ecology. Following centuries of whaling and other emerging threats to their survival including pollution, bycatch and ship-strikes, the conservation status of most rorqual species is difficult to assess due to a shortfall in our knowledge. This thesis aims to facilitate more informed management decision-making and the implementation of more effective conservation measures by bridging key gaps in our knowledge. Pertinent questions on feeding and migration ecology are addressed using intrinsic markers, i.e. chemicals whose stable properties ensure they move through biotic systems and are detectable in tissues. Intrinsic markers include naturally occurring [e.g. stable isotopes, DNA, trace elements] and anthropogenic compounds (e.g persistent organic pollutants or POPs]. In Chapter 1, current knowledge on the ecology of blue [Balaenoptera musculus], fin (R physalus), humpback (Megaptera novaengliae] and minke whales (Racutorostrata] in Irish waters is reviewed. In chapter 2, stable isotope analysis of baleen from these four species is used to approximate the ecological niche and thus to examine resource partitioning. Chapter 3 is a methodological precursor to Chapter 4 where stable isotope Bayesian mixing models are used to investigate the preferred diet of fin and humpback whales in the Celtic Sea. In Chapter 3, unpredictable effects of preanalytical lipid-extraction of skin and blubber biopsies were found for both 513C and <515N values. Chapter 5 is a methodological chapter, concluding that the amount of lipid remaining in blubber biopsies is not representative of blubber in situ. This finding was relevant to Chapter 6 which used POP concentrations to investigate elements of population structure of humpback whales in the North Atlantic. Chapter 7 discusses how the key findings such as the diet preferences of Celtic Sea fin whales (Euphausiids such as Meganyctiphanes norvegica and Nyctiphanes couchii, and year-0 sp ra t [Sprattus sprattus] and herring (Clupea harengusj) and humpback whales (chiefly sprat and herring) may be used to facilitate an informed ecosystem-based approach to fisheries management.