Causes of Mortality in Northern Fur Seals (Callorhinus Ursinus), St. Paul Island, Pribilof Islands, Alaska, 1986–2006

Abstract

ABSTRACT:To determine whether infectious diseases might have contributed to the present-day decline of northern fur seals (Callorhinus ursinus), preweaned pups (n52,735), subadult males (n598), and adults (n5179) were examined postmortem from 1986 to 2006 on St. Paul Island, Alaska. Gross necropsy findings and histologic lesions were used to determine causes of death. Five general categories of mortality were identified for pups: emaciation (1,454 pups, 53%), trauma (497 pups, 18%), perinatal mortality (516 pups, 19%), infectious diseases (82 pups, 3%), and miscellaneous causes (186 pups, 7%). A condition of unknown etiology characterized by multifocal necrotizing myopathy and cardiomyopathy was found in 92 pups. Thirty-three congenital anomalies were identified in 49 pups, including a rare multicentric ganglioneuroblastoma. General linear models were used to examine change in pup mortality and condition (i.e., pup mass) over time. The prevalence of perinatal mortality appeared to increase during the study and relative to past reports. Trauma and infectious conditions appeared to decrease slightly from 1986 to 2006. Although relatively stable during this investigation, emaciation was greater than that reported for past studies. Emaciated pups weighed less than expected during 1988, 1996, and 2004 and more than expected during 1987, 1989, 1990, and 1994 (P#0.003). Average annual weights for all other categories of mortality did not change significantly from 1986 to 2006. Fatal conditions for subadult males included hyperthermia, blunt trauma, entanglement, and bite wounds; nonfatal conditions included seizures, orange discoloration of the blubber, neoplasia, and parasitism. Causes of mortality for most adults included bite wounds with cellulitis and secondary infections, pulmonary edema, dystocia, blunt trauma, and neoplasia. We found no evidence to implicate infectious diseases as a cause in the recent decline of northern fur seals.

A Review of the Welfare Impact on Pinnipeds of Plastic Marine Debris

“…Some examples of "serious scores" to illustrate the range of possible welfare insults causing severe welfare insults based on descriptions of observed seal entanglements from Spraker and Lander (2010); Severe impacts.…”

“…This study found that over two-thirds of entangling materials were derived from fisheries sources. Spraker and Lander (2010) describe the causes of mortality in Northern Fur Seals (C. ursinus) on St. Paul Island, Alaska, and describe some of the horrible combinations of entanglement, asphyxiation and tissue trauma caused by net and packing band loops. In one case described, a living but heavily entangled animal is dragging a dead and decomposing seal in the same piece of net.…”

Antemortem diagnosis of a ventricular septal defect in a California sea lion Zalophus californianus

“…Concurrent bacterial pneumonia in human cardiac patients has been an accepted etiology for myocarditis since the 1940s (Saphir & Amromin 1948), but in small animal medicine, hematogenous spread of septic (usually bacterial, rarely fungal) emboli from pneumonia usually results in endocarditis with vegetative lesions adhered to the mitral and aortic valves (Kittleson 1998b). Multifocal necrotizing myopathy and cardiomyopathy has been described as a cause of death in pups of the northern fur seal Callorhinus ursinus (Spraker & Lander 2010) and affects the left ventricular, and rarely, the right ventricular free walls. The etiology is unknown at this time.…”

Apoptosis in Normal and Coxiella burnetii–Infected Placentas From Alaskan Northern Fur Seals (Callorhinus ursinus)

“…5,8 In a normal placenta, the rate of apoptosis increases throughout gestation; however, apoptosis can also increase in placentas during disease states, such as preeclampsia, intrauterine growth restriction, 6 and placental infections such as Toxoplasma 1 or Listeria. 5 In contrast, C. burnetii has been shown to inhibit apoptosis in host macrophages as a survival strategy.…”

“…3 The decline of the northern fur seal (NFS; Callorhinus ursinus) population on St Paul Island, Alaska, has been well documented but is not easily explained; in a 20-year study evaluating pup mortality, the most common cause of death was trauma and nutrition, with infectious disease only infrequently identified. 8 In 2010, 75% of opportunistically collected NFS placentas from a single rookery were positive for C. burnetii by polymerase chain reaction (PCR). 4 Histologic lesions were infrequent; bacteria was visualized in 5 (3%) of the samples, and only a single placenta had arteritis.…”