Abstract-Understanding the behavior of marine mammals is quite limited by the observation technology used. Surface tracking using either geolocation or Argos satellite tags have shown that these mammals range much farther than previously thought. Relatively simple time/depth recorders (TDR's) have shown dives to depths of over 1000 meters for durations of over one hour. To further the understanding of these aquatic creatures, a smaller and more capable tag is being developed that can be deployed for longer durations and with more sensing capabilities. This tag utilizes a sensor suite consisting of temperature, depth, speed, salinity, three axes of magnetic field, three axes of acceleration, and GPS.The three-axis magnetometers and three-axis accelerometers are used to reconstruct the full attitude quaternion of the creature. Fusing this attitude measurement with water speed, and both initial and final position estimates from GPS, a full three dimensional underwater trajectory can be reconstructed (distributing the error from the return surface as an estimate of the ocean currents). This paper looks at three types of dead reckoning filters used to process this data via simulation: (1) pure open loop integration, (2) "scaled" integration that feeds back measured depth, and (3) a Kalman filter used to estimate the position of the creature, with a correction term from the measured depth (pressure). Comparison of these three navigation filters on simulated data for a 20 minute dive shows that the Kalman filter works best, in terms of position drift, though at the cost of high frequency noise in the trajectory. At the end of a 2 Km path, it shows a total offset error of approximately two meters (or 0.1% drift). The scaled filter is the worst, demonstrating instability at certain points, and the open loop integration yields a position estimate that is off approximately 5 meters at the end of the dive.

The hypothesis of a positive correlation between host specificity and taxonomic diversification was tested in a family of fish ectoparasites, the Diplectanidae Bychowsky 1957 (Monogenea). A comparative analysis of correlation of species richness with host specificity was performed using an adapted independent contrasts method. In order to control for phylogenetic effects, a phylogenetic tree of the genera in the Diplectanidae was reconstructed using morphological characters. The current taxonomy is retrieved in this phylogenetic hypothesis, except for the Murraytrematoidinae subfamily, which appears to be paraphyletic. There is no significant correlation between host specificity and taxonomic diversification in the Diplectanidae. The significance of this result is discussed, and different hypotheses which could have led to this observation are presented.

The aim of this study was to determine if juvenile northern elephant seals, Mirounga angustirostris, translocated from their rookery would return to it quickly and reliably. During the spring and fall of 1990 and 1991 we captured 75 seals at Año Nuevo State Reserve, CA, U. S. A. and translocated them to release sites up to 100 km away. Eighty‐eight percent of the seals returned to the capture site within 4.7 ± 4.3 d. Homing rate increased with age, but even the youngest seals (8–10 mo) homed at a 73% rate. Homing rate did not vary significantly with sex, season, or year. Data from diving instruments suggested that the seals often followed direct routes home, arrived on the rookery significantly more often at night than during the day, and when released together, returned separately. Mean homing speed of 18 seals with complete diving records was 39 km/d (range 3–70 km/d). Instruments on seals had no detectable effect on homing rate or homing speed. The translocation paradigm provides a powerful tool for conducting intensive shortterm studies on free‐ranging seals.

Heart rates of northern elephant seals diving at sea and during apnoea on land were monitored to test whether a cardiac response to submergence is an important factor in their ability to make repetitive, long-duration dives. Seven juvenile northern elephant seals were captured at Año Nuevo, CA, instrumented and translocated to release sites around Monterey Bay. Heart rate and dive depth were recorded using custom-designed data loggers and analogue tape monitors during the seals' return to Año Nuevo. Heart rates during apnoea and eupnoea were recorded from four of the seals after they hauled out on the beach. Diving patterns were very similar to those of naturally migrating juveniles. The heart rate response to apnoea at sea and on land was a prompt bradycardia, but only at sea was there an anticipatory tachycardia before breathing commenced. Heart rate at sea declined by 64% from the surface rate of 107 +/- 3 beats min-1 (mean +/- S.D.), while heart rate on land declined by 31% from the eupnoeic rate of 65 +/- 8 beats min-1. Diving heart rate was inversely related to dive duration in a non-linear fashion best described by a continuous, curvilinear model, while heart rate during apnoea on land was independent of the duration of apnoea. Occasionally, instantaneous heart rate fell as low as 3 beats min-1 during diving. Although bradycardia occurs in response to apnoea both at sea and on land, only at sea is heart rate apparently regulated to minimise eupnoeic time and to ration oxygen stores to ensure adequate supplies for the heart and brain not only as the dive progresses normally but also when a dive is abnormally extended.

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