Black margate

Abstract: Bottlenose dolphins (Tursiops truncatus) are found in the coastal and offshore waters of Puerto Rico. However, little is known about causes of their mortality in the Caribbean. On 18 February 2002, a female bottlenose dolphin was found dead in Bahía de San Juan, Puerto Rico. Remarkably, a black margate (Anisotremus surinamensis) was firmly lodged in the dolphin’s oral cavity and the pharynx. The throat of the dolphin was markedly swollen; the larynx was dislocated; and signs of agonal death were evident. Grossly, the cause of death was determined to be asphyxiation due to choking. Fifty strandings of bottlenose dolphins have been reported between 1937 and 2006 in Puerto Rico and the Virgin Islands. In those for which a cause of death was determined, four were human related and 11 died of natural causes (including this case). The present case study fits the definitions of “choking” and “asphyxiation.” The evolved respiratory anatomy of cetaceans in which the larynx is inserted into the nasal passages leading to the blowhole makes asphyxiation due to choking unlikely in odontocetes. However, if the larynx is irreversibly dislodged from its normal position during swallowing, this may cause the dolphin to stop breathing or even drown. Thus, respiratory blockage from a natural prey item represents an uncommon mortality factor associated with piscivorous cetaceans and is the first record of such marine mammal mortality in the Caribbean.

Abstract: Ages of margate, Haemulon album (n = 415) and black margate, Anisotremus surinamensis (n = 130) were determined using sectioned sagittal otoliths collected from the Southeastern United States Atlantic coast from 1979 to 2017. Opaque zones were annular, forming between January and June for both species, with peaks in occurrence of otoliths with opaque margins in April for margate and March for black margate. The observed ages for margate were 0–22 years, and the largest fish measured 807 mm TL (total length). Black margate ranged in age from 3 to 17 years, and the largest fish was 641 mm TL. Weight–length relationships were: margate, ln(W) = 2.88 ln(TL) − 10.44 (n = 1327, r2 = 0.97, MSE = 0.02), where W is total weight (grams, g); black margate, ln(W) = 3.02 ln(TL) − 11.10 (n = 451, r2 = 0.95, MSE = 0.01). Von Bertalanffy growth equations were Lt = 731 (1 − e−0.23(t+0.38)) for margate, and Lt = 544 (1 − e−0.13(t+2.61)) for black margate. After re-estimating black margate growth using a bias-correction procedure to account for the lack of younger fish, growth was described by the equation Lt = 523 (1 − e−0.18(t+0.0001)). Age-invariant estimates of natural mortality were M = 0.19 y−1 and M = 0.23 y−1 for margate and black margate, respectively, while age-varying estimates of M ranged from 2.93 −0.23 y−1 for fish aged 0–22 for margate and 7.20 − 0.19 y−1 for fish aged 0–18 for black margate. This study presents the first documentation of life-history parameters for margate from the Atlantic waters off the Southeastern United States, and the first published estimate of black margate life history parameters from any geographic region.