Manatee Trichechus manatus latirostris calf mortality in Florida: a retrospective review of pathology data from 2009-2017.

High maternal investment and extended inter-calving intervals in Florida manatees Trichechus manatus latirostris make calf survivorship critical to overall population growth. However, detailed patterns of causes of mortality in calves have not been reported and state agency statistics report portions of perinatal mortality based on body length rather than actual cause of death (COD). The objectives of this study were to categorize COD based on necropsy data and geographical location in Florida for 1209 manatee calf carcasses (<236 cm total length) examined between January 2009 and December 2017 and to describe factors contributing to calf mortality. Results indicated COD was attributed to natural causes (47%, n = 573), cold stress syndrome (38%, n = 457), watercraft injury (13%, n = 155), or other human-related causes (2%, n = 24). Natural causes were the leading COD for small calves <151 cm, with death due to stillbirth or dystocia most frequent (48%, n = 273/573). Enteric trematodiasis contributed to a large proportion of deaths from natural causes in large calves within the southwest region of Florida, with an increasing annual trend. Brevetoxicosis contributed substantially to natural causes within the southwest region exclusively and was commonly comorbid with enteric trematodiasis. Cold stress syndrome was the leading cause of death for large calves (151-235 cm), with the Atlantic region having the highest proportion of cases. Watercraft injury was a sustained threat to large calves, especially within the southwest region. This report provides details on specific health threats and patterns of mortality among manatee calves.

Fatal Blowhole Obstruction by Eel in Common Bottlenose Dolphins (Tursiops truncatus) in Florida, USA.

Esophageal and pharyngeal obstruction are commonly reported in marine mammals, but asphyxiation from blowhole and nasal cavity obstruction has been reported only rarely: in two long-finned pilot whales (Globicephala melas), several harbor porpoises (Phocoena phocoena), and one common bottlenose dolphin (Tursiops truncatus). We describe two cases of blowhole obstruction and subsequent asphyxiation in bottlenose dolphins caused by eels. A whip eel (Bascanichthys scuticaris) was found obstructing the blowhole of a deceased dolphin from the Indian River Lagoon, Florida, US (2011) and a shrimp eel (Ophichthus gomesii) was found obstructing the blowhole of a deceased dolphin from Tampa Bay, Florida (2020). Normally, the respiratory and digestive tracts of cetaceans do not communicate. Consuming large or oddly shaped prey can result in laryngeal displacement and subsequent interaction between the two systems. It is likely the eels entered the oral cavity while the dolphins were consuming or playing with prey, and laryngeal displacement enabled the eels to slither into and become stuck in the nasal passage, causing asphyxiation. These novel findings underscore the importance of continued investigation into causes of mortality in stranded marine mammals and can contribute to the knowledge of feeding ecology in bottlenose dolphins. As changing environmental conditions contribute to shifts in prey availability and abundance, mortality due to prey-related asphyxiation could become more common in odontocetes.

A common bottlenose dolphin (Tursiops truncatus) prey handling technique for marine catfish (Ariidae) in the northern Gulf of Mexico.

Few accounts describe predator-prey interactions between common bottlenose dolphins (Tursiops truncatus Montagu 1821) and marine catfish (Ariopsis felis Linnaeus 1766, Bagre marinus Mitchill 1815). Over the course of 50,167 sightings of bottlenose dolphin groups in Mississippi Sound and along the Florida coast of the Gulf of Mexico, severed catfish heads were found floating and exhibiting movements at the surface in close proximity to 13 dolphin groups that demonstrated feeding behavior. These observations prompted a multi-disciplinary approach to study the predator-prey relationship between bottlenose dolphins and marine catfish. A review was conducted of bottlenose dolphin visual survey data and dorsal fin photographs from sightings where severed catfish heads were observed. Recovered severed catfish heads were preserved and studied, whole marine catfish were collected and examined, and stranding network pathology reports were reviewed for references to injuries related to fish spines. Photographic identification analysis confirms eight dolphins associated with severed catfish heads were present in three such sightings across an approximately 350 km expanse of coast between the Mississippi Sound and Saint Joseph Bay, FL. An examination of the severed catfish heads indicated interaction with dolphins, and fresh-caught whole hardhead catfish (A. felis) were examined to estimate the presumed total length of the catfish before decapitation. Thirty-eight instances of significant trauma or death in dolphins attributed to ingesting whole marine catfish were documented in stranding records collected from the southeastern United States of America. Bottlenose dolphins typically adhere to a ram-feeding strategy for prey capture followed by whole prey ingestion; however, marine catfish skull morphology may pose a consumption hazard due to rigid spines that can puncture and migrate through soft tissue, prompting a prey handling technique for certain dolphins, facilitating consumption of the posterior portion of the fish without the head.