Sink or swim: Risk stratification of preweaning mortality in harbor seal pups (Phoca vitulina richardii) admitted for rehabilitation

Abstract

To date, few consistent relationships between survival in rehabilitation programs and diagnostic measures recorded upon admission have been identified for harbor seal pups. Veterinary records for 718 unweaned Pacific harbor seal pups (Phoca vitulina richardii) admitted to a rehabilitation center were examined to identify clinical factors associated with preweaning survival and develop a triage tool to stratify pups according to their risk of mortality. Physical, serum chemical, and hematological variables were examined and their relationship with survival to weaning was assessed by logistic regression and classification and regression tree (CART) analysis. Survival to weaning was 85.1% and many clinical variables reflecting the pups’ age, size, growth, injuries, and blood parameters were associated with the likelihood of survival. A decision tree model, consisting of serum concentrations of phosphorus, sodium, and calcium, successfully stratified harbor seal pups into clinical subgroups according to their preweaning mortality risk. For both the derivation and validation cohorts, pups classified as “high risk” had significantly lower odds of survival, while those classified as “low risk” had significantly greater odds of survival. This simple decision tree could serve as a practical triage tool to help identify and direct care towards pups at higher risk of preweaning mortality.

Factors affecting the survival of harbor (Phoca vitulina) and gray seal (Halichoerus grypus) juveniles admitted for rehabilitation in the UK and Ireland

“…The high prevalence of malnourishment observed is a cause for concern, as survival analysis showed that the odds of a juvenile seal surviving to release increased by 1.07 times for every kilogram over their age predicted weight, or by 1.11 times per kilogram if the seal is a P. vitulina juvenile (Table 6). This effect is consistent with that previously reported for both P. vitulina (Cole & Fraser, 2021;Harding et al, 2005;MacRae et al, 2011) and H. grypus (Hall et al, 2001(Hall et al, , 2002, where heavier juveniles had higher survival probabilities. This weight dependent survival can most likely be attributed to the importance of fat (i.e., blubber) in thermoregulation (Harding et al, 2005), maintaining an optimal water balance (Rash & Lillywhite, 2019) and buoyancy especially during foraging (Adachi et al, 2014).…”