Quantifying and understanding cetacean bycatch

ICES Annual Science Conference 2023, 11–14 September 2023, Bilbao, SpainFishery bycatch mortality is generally considered to be the main threat to cetaceans in European Atlantic waters. The marine waters in the Northwest of the Iberian Peninsula are among the richest in fishery resources in Europe and, consequently, they are also very important for fisheries. Analysis of cause of death and life history data from strandings in Galicia suggested that the bycatch is a major threat in common dolphins (Delphinus delphis) and harbour porpoises (Phocoena phocoena). The mortality rate in the Iberian population of the harbour porpoise could be well above safe limits. MERMACIFRA (“Monitoring, Assessment and Reduction of Accidental Mortality of Cetaceans due to Interactions with the Spanish Fleet - Review and Action”) is a national Project funded by the Fishery Ministry of Spain, the main objective of which is to monitor, assess and reduce bycatch of cetacean species in Spanish Atlantic waters. This includes acquisition of information on bycaught animals from strandings and on-board monitoring, to quantify bycatch mortality and to build a “profile” of bycaught animals in terms of their sex, size, age, reproductive status and health status. The project collaborates with the Galician stranding network, which attends stranded cetaceans on the Galician coast. Between 1990 and 2020, 3,404 strandings of common dolphins (on average 114 per year) and 344 strandings of harbour porpoises (on average 11 per year) were reported. It was observed that, over the last decade, the number of strandings with bycatch evidence has tended to increase. For 2021, considering only those carcasses examined which preservation state were from fresh to slight (n = 52 for common dolphin, and n = 13 for harbour porpoise), it was obtained that 54% of common dolphins (n = 28) and 23% of harbour porpoises (n = 3) had evidence of fishery interaction. During 2022-2023, we received two notifications from fishers regarding bycaught dolphins. In the first, two common dolphins were collected and studied in the north of Galicia. In the second case, two bycaught common dolphins were thrown overboard by the crew. These data are useful to better understand the reasons for bycatch as well as the resulting mortality. MERMACIFRA also aim to assess methods to reduce bycatch in nets and purse seine fisheries (e.g., using net modifications and observers on-board). Pilots using three types of acoustic deterrent devices indicates different efficacy depending on the species and fisheryN

Capturado y registrado: potencial de las redes de varamientos para el estudio de las capturas accidentales de cetáceos

XII Congreso de la Sociedad Española de Cetáceos, 4 al 7 de octubre de 2021, onlineN

Descifrando la dieta de las principales especies de cetáceos odontocetos en aguas de Galicia: 30 años de estudio

XIII Congreso de la Sociedad Española de Cetáceos (SEC), Eivissa, 27 – 30 octubre 2022N

From Galician waters to cetacean stomachs, a feeding story told by preys

34th European Cetacean Society Conference, O Grove, 16-20 April 2023Cetaceans play an important role in maintaining the health and stability of marine ecosystems. To understand the trophic relationships of these top predators in waters off the Northwest Iberian Peninsula, and to determine their possible competition with fisheries, the stomach contents of 751 common dolphins (Delphinus delphis), 60 striped dolphins (Stenella coeruleoalba), 124 bottlenose dolphins (Tursiops truncatus), and 72 harbour porpoises (Phocoena phocoena) stranded on the Galician coast between 1990-2018 (almost 30 years) were analysed. Results indicated that their diets are mainly piscivorous (after identified 90 different taxa: 68 fish and 22 cephalopods), being the blue whiting (Micromesistius poutassou) and the European hake (Merluccius merluccius) the most important preys (in occurrence, number, and biomass) throughout all the years studied and for the four cetacean species. The long time series available allowed to detect interannual variation in the diet of both common dolphins and harbour porpoises by means of Generalised Additive Models (GAMs), observing an increase in the presence of European hake and a decrease of sardines (Sardina pilchardus) in the stomachs through time. Seasonal variation in the diets of the common and striped dolphins were also observed, with a higher consumption of blue whiting during the summer (May-September). Significant differences were found in the diet of the two bottlenose dolphin ecotypes present in Galicia, the coastal ecotype contains a higher percentage of demersal preys in the stomachs, while the oceanic ecotype contains more pelagic preys, confirming the habitat separation between the two. Results also confirmed an ontogenic variability in the diet of harbour porpoises, with juvenile animals showing a higher presence of coastal preys in the diet (e.g., pouting – Trisopterus luscus). There is an overlap between the diet of these four cetacean species and the fisheries‟ target species in the area, indicating competition for some resourcesN

Preliminary delimitation of areas of interest for the bottlenose dolphin (Tursiops truncatus) and the harbour porpoise (Phocoena phocoena) in Galicia (NW Spain)

2 pages, 2 tables, 1 figure.-- Fifteenth Annual Conference of the European Cetacean Society, Rome, Italy, 6-10 May 2001The presence of the bottlenose dolphin (Tursiops truncatus) and the harbour porpoise (Phocoena phocoena) in the coastal waters of Galicia (NW Spain) is very well documented for hundreds of years. However, there is a lack of knowledge conceming their abundance, distribution, and habitat useN

Age and growth of stranded common dolphin (Delphinus delphis), striped dolphin (Stenella coeruleoalba) and harbour porpoise (Phocoena phocoena) along the Galician coast (NW Spain)

1 page.-- Fifteenth Annual Conference of the European Cetacean Society, Rome, Italy, 6-10 May 2001A total of 673 cornmon dolphins (Delphinus delphis), 82 striped dolphins (Stenella coeruleoalba), and 101 harbour porpoises (Phocoena phocoena) were found stranded along the Galician coast between 1990 and 1999. Tooth samples from 108 cornmon dolphins, 17 striped dolphins and 16 harbour porpoises were analysed for ageing studies. Methods for these purposes were adapted from Hohn & Locþer (199s). Teeth were cleaned with a 5% pepsin solution and then soaked in the decalcifying agent RDO. Sections were cut at 20 mm using a freezing microtome. Optimum sections were selected from each tooth for counting annual ringsN

Marine mammal and fisheries interactions in Galicia, north-west Spain

23rd Annual Conference of the European Cetacean Society,“Climate Change and Marine Mammals”, Istanbul, Turkey, 2-4 March 2009Galicia, north-west Spain, is one of the world’s main fishing regions and fishing is an important component of the economy. Previous interview surveys with fishermen five and ten years ago highlighted a high (up to 1700 cetaceans per year) and potentially unsustainable cetacean by-catch rateN

Small cetacean distribution in North Atlantic Iberian Peninsula waters 2007-2019

34th European Cetacean Society Conference, O Grove, 16-20 April 2023Information on cetacean distribution is needed at a range of scales, such as European, national, subregional or regional level. Providing detailed information at larger scales, with the highest possible spatial resolution, is essential to adequately assess and evaluate the impacts of human activities at the population or subpopulation level, as required by several legal instruments and international agreements (e.g., OSPAR or ASCOBANS). In this study, we modelled the distribution and relative abundance of common dolphin (Delphinus delphis), bottlenose dolphin (Tursiops truncatus), and pilot whale (Globicephala melas) in continental shelf waters of the Spanish North Atlantic waters, using a time series of 13 years of sightings collected on the PELACUS multipurpose survey in spring months by means of Distance Sampling methodology. Species distribution models were fitted using geographical and biological explanatory variables. The more than 20,000 km of effort, regularly distributed over the study area throughout the time series, provided more than 400 sightings of the species of interest. The three species showed interannual variability in distribution and relative abundance. These annual differences might reflect changes in their movement patterns due to the different timing of oceanographic and biological processes between years, as shown by the models and the variables analysed. The results prove the relevance of the continental shelf in southern Galicia (the Rias Baixas) as an area of importance for these species. The maps produced have several applications, including the identification of relevant areas for these species and, when combined with other data (e.g., fishing effort, underwater noise), quantitative risk analysis to different anthropogenic activitiesN

Variability in the diet of common dolphin (Delphinus delphis) in Galician waters 1991-2003 and relationship with prey abundance

19th Annual Conference of the European Cetacean Society and associated workshop, April 2-7, 2005, La Rochelle, FranceAnalyses of marine mammal diets in Galician (NW Spain) waters have been carried out over the last 13 years as part of four consecutive European funded projectsN