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Diving development in nursing harbour seal pups

Christian Jørgensen^1,2, Christian Lydersen¹, Ole Brix² and Kit M. Kovacs^1,*

¹ Norwegian Polar Institute, Polar Environmental Center, N-9296 Tromsø, Norway and
² Department of Zoology, University of Bergen, Allégaten 41, N-5007 Bergen, Norway

View larger version (58K): [in a new window]   Fig. 1. Map of Svalbard (inset) with Prins Karls Forland enlarged. Pups with time/depth recorders were captured and recaptured in the hatched area around Forlandsøyane, except for pup 1999-09, which was captured and recaptured in the hatched area towards the southern tip of the island. All other animals included in the study were caught along the western coast of Prins Karls Forland.

View larger version (26K): [in a new window]   Fig. 2. Body composition of harbour seal pups captured serially (twice) on Svalbard (N=8). ‘Fat’ (open columns) is total body fat, ‘Blood’ (shaded columns) is total blood volume and ‘Lean body mass’ (hatched+shaded columns) is fat-free body mass.

View larger version (14K): [in a new window]   Fig. 3. Frequency distribution of dive depths (A) and dive durations (B) for 6027 dives recorded by time/depth recorders deployed on 13 harbour seal pups on Svalbard. Values are means + S.D.

View larger version (20K): [in a new window]   Fig. 4. (A) The proportion of time spent in the water (y) versus pup age (x) (y=24.3+2.57x, r2=0.20). (B) Maximum daily swimming speed versus pup age (y=1.109+0.027x; r2=0.10). (C) Average daily swimming speed versus pup age (slope of regression not significant). The numbers above the error bars in A–C correspond to the number of pups for which data were recorded. (D) Proportion of dives of 6 m or deeper (N=1118) that were classified as U-dives by cluster analysis versus pup age (y=0.192+0.022x, r2=0.59). The numbers above the data points in D are the total number of U-dives performed by pups of the given age. Dive characteristics were measured using time/depth recorders deployed on 13 nursing harbour seal pups on Svalbard, Norway. Error bars are ±1 S.D.

View larger version (14K): [in a new window]   Fig. 5. Haematocrit versus pup age for harbour seals on Svalbard (linear regression for pups more than 5 days old: y=49.2+0.23x, r2=0.20). The eight pups that were sampled twice are represented by individual symbols; open circles represent additional pups.

View larger version (13K): [in a new window]   Fig. 6. (A) Plasma volume and the corresponding blood volume calculated from haematocrit expressed as absolute volumes (ml). (B) Plasma volume and the corresponding blood volume calculated from haematocrit expressed as a percentage of body mass. (C) Total body fat (kg) measured by hydrogen isotope dilution. Symbols represent individual pups, and all lines are for illustrative purposes only.