Use of stomach temperature telemetry to quantify ingestion by Phocid seals

Hedd, April (1994) Use of stomach temperature telemetry to quantify ingestion by Phocid seals. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (10MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

The applicability of using stomach temperature probes to investigate the feeding behaviour of seals was tested. Captive harp seals (Phoca aroenlandica) were fed stomach temperature sensors and given pre-weighed meals of herring (Clupea harengus) and crushed ice. Ingestion of either substance caused a decrease in stomach temperature (see also Gales and Renouf 1993). Results suggested that the magnitude of stomach temperature change could indicate whether the ingested substance was a prey item or ice. The duration of stomach temperature change was significantly related to the quantity of fish consumed, but it accounted for just 27% of the overall variation. This percentage was much less than the 71% reported by Gales and Renouf (1993), perhaps due in part to the larger sample size used in the present study. Prey temperature was a significant covariate in the relationship between meal mass and the corresponding duration of stomach temperature change, but, overall it added very little to predictive power. Both the magnitude and duration of the temperature change were related to the quantity of ice consumed, accounting for 69% of the variation. Subsequent modelling of this relationship, however, revealed that it was not robust. Monitoring the stomach temperatures of wild seals would tell us little about the quantity of prey consumed, however, when used in conjunction with satellite-linked time-depth recorders they could provide valuable on the location, timing and frequency of prey consumption. -- A harbour seal (Phoca vitulina) mother and pup were fed stomach temperature probes throughout the lactation period. Behavioural observations were conducted while stomach temperature was concurrently logged. Milk intake caused a decrease in the pup's stomach temperature, and the duration of this temperature change was related to the length of the nursing bout. Laboratory stomach simulations, which suggested a strong relationship between milk volume and the subsequent duration of temperature change, were used to estimate the volume of milk consumed by the pup. Suckling bout length and the estimated milk intake per bout increased as a weekly average over the five week lactation period. A temporal change in the suckling pattern was noted, with a progression from largely nocturnal to daytime feedings. Although not visually confirmed, temperature data collected from the mother provided evidence of seawater ingestion. Direct pup feeding experiments using known quantities of the mother's milk, at a known temperature, would greatly improve the accuracy of these intake estimates. -- These studies indicate that, with sufficient samples, stomach temperature probes may provide a valuable tool for investigating lactation energetics and other aspects of the feeding ecology of marine endotherms.

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