Opportunistic gillnet depredation by common bottlenose dolphins in the southwestern Gulf of Mexico: Testing the relationship with ecological, trophic, and nutritional characteristics of their prey

Competition between fisheries and bottlenose dolphins is a globally relevant conflict given its socioeconomic and ecological implications. Understanding the factors driving the interactions between dolphins and fishery activities is key to the development of appropriate mitigation strategies. Our study aimed to assess whether these interactions are related to the ecological, trophic, and nutritional characteristics of the catch. We used 117 gillnet sets from 48 fishing trips during 2009 – 2010 and 2015 – 2019, which were classified based on the presence or absence of dolphin interactions. These interactions occurred year-round and were documented in 46.1% of the sets, with 14.5% of those showing signs of depredation. The passive acoustic predatory hypothesis, which states that fish species that generate sound are subject to a higher predation intensity by dolphins, was not supported by our data. Also, with the exception of species diversity, ecological parameters such as richness, biomass and CPUE were slightly higher, although not significant in sets with dolphin interaction. Furthermore, during 2015 – 2016, we sampled 123 organisms of 25 representative fish species in the catches and determined the whole fish isotopic composition (δ13C and δ15N), and estimated the nutritional value (i.e., lipid, protein, and energy content) of each species. Isotopic values showed no differences between net settings (with and without interaction), fish habitat, or prey type (potential prey, n= 11 species, vs. non-potential prey, n= 14). However, a preference towards fish from a certain range of thropic levels was evident. All the fish (N= 123) showed significantly higher protein values during the Rainy period, which may be attributed to their reproductive cycles and higher primary productivity. Interestingly, energy contents of the dolphins’ potential prey were also significantly higher during this period. Unexpectedly, protein and energy contents were significantly higher in the fishes caught in the sets without dolphin interaction, but only during the Dry and Windy periods, respectively. Opportunistic feeding habits are well known for bottlenose dolphins, and our results showed that “easy access” to prey will likely prompt interaction with gillnets, regardless of the species composition, biomass, seasonality, preferred habitat, sound production capacity, or nutritional value of the captured fish

Ecología social de los delfines (Tursiops truncatus) en las aguas costeras de Alvarado, Veracruz, México

Tesis presentada al Instituto de Ciencias Marinas y Pesquerías de la Universidad Veracruzana, Región Veracru

Phenotypic variation in dorsal fin morphology of coastal bottlenose dolphins (Tursiops truncatus) off Mexico

Geographic variation in external morphology is thought to reflect an interplay between genotype and the environment. Morphological variation has been well-described for a number of cetacean species, including the bottlenose dolphin (Tursiops truncatus). In this study we analyzed dorsal fin morphometric variation in coastal bottlenose dolphins to search for geographic patterns at different spatial scales. A total of 533 dorsal fin images from 19 available photo-identification catalogs across the three Mexican oceanic regions (Pacific Ocean n = 6, Gulf of California n = 6 and, Gulf of Mexico n = 7) were used in the analysis. Eleven fin shape measurements were analyzed to evaluate fin polymorphism through multivariate tests. Principal Component Analysis on log-transformed standardized ratios explained 94% of the variance. Canonical Discriminant Function Analysis on factor scores showed separation among most study areas (p < 0.05) with exception of the Gulf of Mexico where a strong morphometric cline was found. Possible explanations for the observed differences are related to environmental, biological and evolutionary processes. Shape distinction between dorsal fins from the Pacific and those from the Gulf of California were consistent with previously reported differences in skull morphometrics and genetics. Although the functional advantages of dorsal fin shape remains to be assessed, it is not unlikely that over a wide range of environments, fin shape may represent a trade-off among thermoregulatory capacity, hydrodynamic performance and the swimming/hunting behavior of the species

Introduction to the Special Volume on Tursiops in the Southwest Atlantic Ocean

LAJAM Special Volume on Tursiops in the Southwest Atlantic Ocean is introduced

Trends and gaps in marine mammal research from Mexico during 1998 – 2021

Marine mammals are very diverse because of the oceanographic conditions of Mexican waters (where 36% of the current species worldwide are found); however, scientific research on many of these taxa is still at the basic stages. The goal of this study was to assess the scientific information available for these species and to determine research priorities through a GAP (from the acronym "Good", "Average", and "Poor”) analysis. Information from the abstracts of the meetings held by the Mexican Society of Marine Mammalogy (SOMEMMA) and online databases (SCOPUS and Web of Science) between 1998 and 2021 was analyzed using temporal (years), geographic (oceans or states), taxonomic (species), and thematic (topics) classifications. On average, of the 44 species included in the Mexican legislation, only 16 - included in 14 families (with most of the records) - are studied every year, Delphinidae (n = 500; 25.9%), Balaenopteridae (n = 335; 17.4%), and Otariidae (n = 316; 16.4%). The Gulf of California was the most studied region (35.4%), followed by the Northeast Pacific (19.3%), the Gulf of Mexico (15.5%), and the Caribbean Sea (6.9%). The most frequent topics were population ecology (32.9%), conservation (16.7%), and animal health (10.4%). A significant decrease in the taxonomic and thematic diversity of such studies has been noted since SOMEMMA meetings began to be held on a biennial basis. It is noteworthy that marine mammals are protected by Mexican Federal laws. However, stock assessments are not mandatory, therefore biological aspects and trends of several (mostly oceanic) species remain unknown in many places, especially in regions where academic and scientific institutions are not involved in marine science

Possible Stock Structure of Coastal Bottlenose Dolphins off Baja California and California Revealed by Photo-Identification Research

Volume: 114Start Page: 1End Page: 1

Interannual shifts in sea surface temperature and chlorophyl drive the relative abundance and group size of common bottlenose dolphins Tursiops truncatus on the Southeast Gulf of California

Despite being one of the most common odontocetes off Sinaloa (Mexican Pacific coast), basic studies on the ecology of common bottlenose dolphins (Tursiops truncatus) are scarce in the region. This study aimed to describe changes in the relative abundance, group size, and behavior of this species during 2007 – 2012. We used boat-based surveys and satellite images of sea surface temperature (SST) and chlorophyll-a (Chl-a) to model changes in dolphin relative abundance (RA) over time, using correlations in time series analyses. Overall, mean RA was 3.6 dolphins h-1 (SD = 8.0), and significantly higher RA (6.4 –16.7 dolphins h-1) occurred in 2008, 2011, 2012, which was concurrent with hydrographic effects of La Niña oceanographic conditions, as well as during the upwelling season (February – April) (SST: 17.3 – 25.0 °C; Chl-a: 3.7 – 21.4 mg m-3). Conversely, significantly lower RA values (0.5 – 3.8 dolphins h-1) occurred in 2007 and 2010 that were likely associated with El Niño effects on the biological productivity of the area (Chl-a: 0.3 – 7.6 mg m-3). We found significant correlations between monthly Chl-a and SST average values with mean bottlenose dolphins RA, and lags (22 – 29 days) in the trophic response to variations of the hydrographic parameters. Significantly larger dolphin groups were recorded during La Niña years possibly because of the higher availability of their prey. This hypothesis is supported by higher feeding frequencies (35 – 73%) observed during the upwelling seasons, especially during La Niña conditions, whereas the most frequent behavior throughout all other years was traveling (28 – 69%). Our results show that RA and group size of bottlenose dolphins inhabiting the waters off Sinaloa, Mexico, are likely influenced by the changes in hydrographic parameters, especially during extreme climatic events