# Pathology and Cause of Death in Stranded Kogiids: A Retrospective Study from the Canary Islands (1999–2018)

## TL;DR

This study examines 45 stranded pygmy and dwarf sperm whales in the Canary Islands to determine causes of death and health issues, finding heart disease, parasites, and human-related factors as major contributors.

## Contribution

The study provides the first comprehensive pathological assessment of kogiids, identifying novel infections and health patterns in these rarely studied whales.

## Key findings

- Heart disease and cardiac lesions were prevalent in 68.9% of stranded kogiids.
- Human-related causes like ship strikes and plastic ingestion accounted for 24.4% of deaths.
- Parasitic infections such as Anisakis sp. and Crassicauda sp. were frequently observed.

## Abstract

Pygmy and dwarf sperm whales are deep-diving cetacean species that are rarely seen alive. Therefore, most knowledge about their health comes from stranded animals. In this study, we examined 45 stranded whales from the Canary Islands over a 20-year period to elucidate the causes of death and associated diseases. Most deaths were attributed to natural causes, especially injuries caused by interactions with other animals, infections, parasites, and heart disease. Many whales exhibited long-standing cardiac lesions, reiterating heart disease as a common health problem in these species. Parasitic infections of the stomach and the cervical-gill gland were also frequent. Human activities were responsible for a considerable number of deaths, mainly from ship strikes, fishing gear interactions, and ingestion of plastic debris. Various infections and pathologic findings identified in this study had not been previously reported in these whales. Overall, these findings improve understanding of the health problems affecting these little-known whales and highlight the importance of post-mortem examinations to support research informing conservation and protection strategies.

The scientific understanding of cetacean pathology has advanced significantly in recent decades. However, data concerning the health status of members of the family Kogiidae remains scarce. This study presents a comprehensive pathological assessment and determination of causes of death in 45 stranded kogiids, comprising 35 Kogia breviceps and 10 K. sima, along the coasts of the Canary Islands between 1999 and 2018. Causes of death (CD) were classified as natural (30/45; 66.6%) or anthropogenic (11/45; 24.4%), while the cause remained undetermined in four cases (9%). Among natural causes, the most prevalent etiologies included trauma (13/30; 43.3%), infectious (7/30; 23.3%), parasitic (5/30; 16.6%), cardiomyopathy (3/30; 10%), malnutrition (1/30; 3.3%), and fetal distress (1/30; 3.3%). Anthropogenic causes were vessel collisions (7/11; 63.6%), interactions with fishing activities (2/11; 18.2%), and foreign body-associated pathology (2/11; 18.2%). Notably, intra- and interspecific traumatic interactions were frequently identified in this cohort, and variable degrees of gross and histologic cardiomyopathic changes were observed in 68.9% of individuals (31/45) without evident sex bias. Septicemia caused by Clostridium perfringens and C. tertium was confirmed in three cases. Additionally, cervical gill slit adenitis by Crassicauda sp. (15/45; 33%) and parasitic gastritis by Anisakis sp. (27/45; 60%) were frequent findings. These findings provide novel insights into the pathologic spectrum affecting kogiids and enhance the current understanding of their health status, with implications for diagnostic protocols, stranding response, and conservation strategies.