Sink or swim: Risk stratification of preweaning mortality in harbor seal pups (Phoca vitulina richardii) admitted for rehabilitation
Justine Cole and David Fraser
Orphaned harbor seal pups constitute a large number of the patients admitted to marine mammal rehabilitation centers. While veterinary care has advanced in recent years, not all of these pups will survive to be released back into the wild. To further understand what determines if a pup will “sink” or “swim”, we examined the physical condition, growth, injuries, and blood results of newborn harbor seal pups admitted for rehabilitation. From these factors, we built a decision tree that is able to identify pups at greater risk of mortality. This, in turn, may help rehabilitators direct care toward pups with the poorest prognosis.
Gear modifications reduced humpback whale entanglements in a commercial rock lobster fishery
Jason R. How, William K. de la Mare, Douglas K. Coughran, Michael C. Double, Simon de Lestang
A study by Australian researchers has demonstrated that fishing gear modifications have significantly reduced humpback whale entanglements in the West Coast Rock Lobster Managed Fishery. The fishery shares the coast with an ever-increasing humpback whale population. Increased whale entanglements in lobster fishing gear from 2011-2013 prompted research into ways to mitigate these interactions. The implementation of several measures, including reduced floats and rope length, and the elimination of surface rope in deeper water, saw entanglements drop by ~60%. This is the first time gear modifications have been shown statistically to reduce entanglements with this iconic species.
Contrasting trends in gray seal (Halichoerus grypus) pup production throughout the increasing northwest Atlantic metapopulation
Cornelia E. den Heyer, W. Don Bowen, Julian Dale, Jean‐François Gosselin, Michael O. Hammill, David W. Johnston, Shelley L. C. Lang, Kimberly T. Murray, Garry B. Stenson, Stephanie A. Wood
The northwest Atlantic gray seal has been increasing for more than a half century. In 2016, total pup production was estimated at all breeding colonies in Canada and the U.S. to be about 110, 000 pups. Sable Island accounts for 80% of the pup production. Regional differences in pup-production trends are evident, with the most rapid increase in the more recently established colonies in the Gulf of Maine and Nantucket Sound. As gray seal populations continue to increase, we should expect this large marine predator to play an increasingly important role in continental shelf ecosystems.
Environmental drivers of habitat use by common bottlenose dolphins (Tursiops truncatus) in the Indian River Lagoon, Florida, USA
Rachael Greller, Marilyn Mazzoli, Elizabeth Titcomb, Brandy Nelson, Richard Paperno, Scott H. Markwith
Human impacts in estuaries can influence the habitat use, health, and continued presence of marine mammals. Our objective was to examine the influences of variability in environmental factors and prey availability in 2003-2015 on habitat use of bottlenose dolphins living in Indian River Lagoon (IRL), Florida. We utilized photo-identification surveys to calculate dolphin density across the IRL in wet and dry seasons each year, and sampled prey and environmental factors monthly. Dolphin density was influenced by salinity and dissolved oxygen levels, which are associated with freshwater discharges of nutrient and algae laden waters from the region’s storm water management system.
A multidecadal Bayesian trend analysis of harbor porpoise (Phocoena phocoena) populations off California relative to past fishery bycatch
Karin A. Forney, Jeffrey E. Moore, Jay Barlow, James V. Carretta, Scott R. Benson
Bycatch – or accidental death in fishing gear – has affected dolphins and porpoises in many coastal regions worldwide. Off California, three harbor porpoise populations experienced substantial bycatch in nearshore gillnet fisheries during the 1970s-1980s. Our analysis of 1986-2017 aerial survey data reveals that all three populations are recovering after gillnets were eliminated. The southern-most Morro Bay population appears to have been affected to a much greater extent than previously recognized, growing from 570 porpoises to nearly 4,200 during our study. These results offer hope that other threatened dolphin and porpoise populations worldwide can also recover if bycatch is eliminated.
Age estimation and growth layer patterns in teeth of crabeater seals: A comparison of techniques
Julieta Cebuhar, Javier Negrete, Silvina Botta
Reading ages in teeth is a common technique that provides important information about ecological and life-history parameters. We applied and compared two techniques for age estimation in crabeater seals. We also evaluated the effects of cleaning teeth with H2O2 on GLG readings. Boiling with H2O2 affected cementum structure and thus resulted in underestimated ages, and must be avoided. Ages can be estimated regardless of which tooth/tissue or method is used for seals <13 years old. However, we recommend counting GLGs in the cementum of nontreated, stained thin sections of postcanine teeth for older animals.
Variation in trophic resources in female South American sea lions at a small geographic scale
M. Florencia Grandi, Damián G. Vales, Enrique A. Crespo, Rocío Loizaga
This study explores the isotopic niche of South American sea lion (SASL) females in the last period of the pregnancy from different colonies of northern Patagonia and considers whether the fine scale genetic spatial structuring is potentially related to variation in trophic resources. Differences among colonies revealed the plasticity of the species and support individual trophic specialization of SASL females at a small geographic scale. Also, significant differences were found between the north and south zones. Several hypotheses were proposed to explain the differences in SASL females’ isotope values (e.g., use of different foraging areas or prey, isotopic baseline variation).
Abundance, survival, and annual rate of change of Cuvier’s beaked whales (Ziphius cavirostris) on a Navy sonar range
K. Alexandra Curtis, Erin A. Falcone, Gregory S. Schorr, Jeffrey E. Moore, David J. Moretti, Jay Barlow, Erin Keene
Cuvier’s beaked whales are sensitive to Navy sonar, yet a population of regularly occurring individuals uses a Navy training range off Southern California. We assessed the population growth rate, abundance, and survival of this group of animals with photo-identification data collected over 11 years. Our results support the existence of a small local resident population mixed with transients. We did not see evidence of a population decline, but our sample size remains limited and uncertainty high. Simulations of future sampling scenarios show that further monitoring and increased effort would substantially increase our ability to detect declines in the future.