ABSTRACT Bycatch in fisheries is a primary threat to small cetaceans, but its true magnitude is often underestimated, particularly in regions with less thorough stranding response networks. Advanced decomposition of stranded carcasses often obscures evidence of fisheries interaction, masking the actual rate of anthropogenic mortality. Here, we quantify fisheries interactions affecting small cetaceans along the Southern Brazilian coast and estimate cryptic mortality masked by decomposition. We analyzed data from 321 necropsied cetaceans collected by the Santos Basin Beach Monitoring Project (PMP‐BS) from 2016 to 2019, focusing on the Franciscana dolphin ( Pontoporia blainvillei ) and the common bottlenose dolphin ( Tursiops truncatus ). A high fisheries interaction rate (68%) was observed among the 25 well‐preserved carcasses. However, most carcasses were found in an advanced state of decomposition, precluding direct analysis. Extrapolating this interaction rate to decomposed P. blainvillei carcasses increased the estimated number of bycaught individuals from 68 to 182, indicating that mortality may be severely underreported. Our results highlight that decomposition masks the actual impact of fisheries, which is likely far greater than currently recorded. This extrapolation approach provides a crucial tool for more realistic mortality assessments.
ABSTRACT Assessing foraging behavior of harbor porpoise ( Phocoena phocoena ) from acoustic data has become increasingly common. Yet, a wide range of analytical methods is currently used, often without formal evaluation of their comparability. This lack of cross‐method validation limits the ability to compare findings across studies and interpret differences in reported foraging activity. This study addressed this challenge by providing a systematic comparative evaluation of acoustic foraging detection methods, while introducing a novel refinement, the Search Buzz Foraging Identification (SBFI) method. We aimed to quantify the degree of similarity of the SBFI method alongside four established methods that use acoustic data and more specifically inter‐click intervals to identify foraging behavior. All methodologies were applied to the same F‐POD dataset collected at two locations for a full year. Comparability among methods was evaluated using correlation, distance, and trend analyses to assess agreement in relative patterns, absolute magnitude, and temporal dynamics. Most methods indicated strong agreement in relative foraging patterns and temporal trends; however, differences in magnitude and context‐dependent biases emerged under specific spatial or seasonal conditions, suggesting methods are not completely interchangeable. The SBFI method showed strong correlation with several existing methods while providing a comprehensive and accessible framework for identifying foraging behavior. This study gives a systemic overview of existing foraging metrics and provides a basis for improved comparability and interpretation of acoustic‐based foraging studies.
ABSTRACT This study evaluated reproductive parameters and growth patterns of male and female franciscana dolphins, Pontoporia blainvillei , in Santa Catarina State, southern Brazil, between Franciscana Management Area (FMA) II and III. We analyzed ovarian and testicular characteristics, counted the tooth growth layer groups, and constructed growth curves. For reproductive parameters and sexual maturity, the gonads of 112 franciscanas (58 females, 54 males) and teeth of 105 specimens (55 females, 50 males) were analyzed; and to estimate age and growth patterns, 297 individuals were analyzed (171 males, 126 females). All samples were collected from the monitoring of strandings on beaches between August 2015 and August 2020. Ovulation corpora were found in 20 females (34.5% mature) and in 38 individuals they were absent (65.5% immature). Histological analysis of the testes showed that 34 males were immature (63%) and 20 were mature (37%). Application of the Gompertz growth model identified distinct growth patterns between the sexes. While both showed an initial rapid phase, females attained a significantly larger asymptotic length (145.5 cm) than males (125.1 cm) and reached it at a later age (7 years vs. 5 years). These data will be useful in comparing reproductive parameters among FMAs.
ABSTRACT Growth curves provide critical biological context for understanding life history, population dynamics, and responses to environmental change, yet our understanding of age–length relationships for humpback whales ( Megaptera novaeangliae ) remains largely based on measurements collected during commercial whaling operations from the mid‐20th century. These measurements may not reflect the growth trajectories of present‐day populations that have undergone substantial recovery and ecological change. Here, we establish contemporary, population‐specific, growth curves for eastern Australian humpback whales (breeding stock E1) using noninvasive aerial photogrammetry coupled with photo‐identification sighting histories. Total length measurements were collected from 865 individually identified whales between 2021 and 2024 and for a subset of these individuals, minimum age estimates were derived from long‐term photo‐identification sighting histories. Bayesian growth models were fitted to evaluate age–length relationships across multiple growth functions and age formulations. Growth was rapid during early life and approached an asymptotic adult length consistent with historical estimates for humpback whales in Australia. Predicted length at age 5 (median 10.93 m) and the age at which whales reached 90% of asymptotic length (median 6.58 years) indicated faster juvenile growth and earlier attainment of near‐adult size than reported elsewhere for contemporary Northern Hemisphere populations. The growth parameters and length‐at‐age estimates provide a baseline for demographic inference. Further, they support long‐term monitoring of growth and energetic constraints in a humpback whale population that has undergone one of the most rapid recoveries documented in a large whale species and is experiencing ongoing environmental change.
ABSTRACT The costs and benefits of group living can influence animal group size and social relationships, and these balance points may shift as animals mature. Young male sperm whales ( Physeter macrocephalus ) appear to form stable all‐male groups unrelated to direct defense of females or territories, but quantitative data on how sociality changes with growth are limited. We examined associations among individually identified males in the Goto Submarine Canyon and Nemuro Strait, Japan, and tested whether social relationships varied with body length. Smaller males showed higher association indices, and both association strength and maximum association index declined with increasing body length. The decline occurred around 13–14 m, near the size at which males typically reach sexual maturity. Standardized lagged association rates indicated both temporary and longer‐lasting associations among smaller males in the Goto Submarine Canyon. These results are consistent with a reduction in male sociality during growth, likely reflecting changing physiological state and shifting ecological costs and benefits of sociality. Increased energetic demands, improved individual foraging capacity, and reduced predation risk in larger males may all contribute to weaker associations with increasing size.
