A 33-test neurological exam built for harbor seal pups in rehabilitation

The researchers examined 45 stranded pups over 2 consecutive years. After the first year, they revised their draft into a 33-test exam. Many of the tests come from the small animal neurological exam, and others were designed around how seal pups' bodies work.

New elements include a sloped ramp to assess proprioception and motor function, a "handstand" to check neck reflexes, and a fish head hung above the pup. The fish head tests balance, strength, coordination, and cranial nerve function, including visual field. The team started with a metal nut but switched to a fish head after some pups tried to bite the nut.

To check reliability, the team repeated the exam on 17 pups. Of the 33 tests, 26 gave a dependable result in at least 80% of those exams. Some pups' temperaments made certain results hard to interpret. The authors suggested the protocol could be adapted for other phocid seals.

In 3 pups with suspected neurological deficits, the exam correctly localized the lesion. Imaging, necropsy, or both later confirmed the location in each case.

In one pup with poor balance and coordination, MRI showed middle ear fluid consistent with otitis media and a spinal cord lesion at C1-C2. The authors said either finding could have affected balance. The pup improved on antimicrobials and was released. Imaging found porencephaly in another pup and severe hydrocephalus in a third.

Three pups that appeared weak on repeat exams were diagnosed with primary malnutrition. The authors considered their deficits secondary to systemic illness. All 3 recovered enough to be released.

The exam is part of a broader program, involving Texas A&M veterinary toxicologist Todd O'Hara, that studies contaminants in marine mammals along the Pacific Coast. Mercury becomes more concentrated at each step up marine food webs, and pups can be exposed through the placenta and through milk.

A 2021 study at the same center measured total mercury in blood and hair from 267 harbor seal pups admitted between 2015 and 2019. Some of the hair was lanugo, the coat pups grow in utero. Higher mercury levels were linked to weaker responses to touch, reduced movement, and longer rehabilitation stays. The researchers described the associations as modest but statistically significant, with wide variation between pups. Mercury levels showed no relationship with survival.

According to Texas A&M, the group plans to study California sea lions in Mexico next. It also plans to continue community-based work on mercury and other trace elements with harbor seals in Alaska.