Index%20to%20Patch%20Quality%20(IPQ)%20Applied%20to%20Yearling%20Steller%20Sea%20Lions%20in%20Alaska

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Index to Patch Quality (IPQ) Applied to Yearling
Steller Sea Lions in Alaska
J Ward Testa National Marine Mammal
Laboratory c/o Biological Sciences - UAA 3211
Providence Dr Anchorage, AK 99508
Jennifer M Burns Department of Biological
Sciences University of Alaska Anchorage 3211
Providence Dr Anchorage, AK 99508
Summary Mori and Boyds (2004) Index of Patch
Quality was applied to dive shapes obtained by
satellite telemetry from 14 yearling Steller sea
lions. In a record lasting from Nov-July, there
was a significant seasonal peak in IPQ and
predicted net rate of energy intake during dives
in Nov-Jan, and a nadir in Apr-Jun. Results
suggest the approach is worth pursuing,
particularly toward better understanding of the
performance and potential for artifacts in IPQ
calculations, and field validation of IPQ
measures.
Introduction Mori and Boyd (2004) formulated and
applied an IPQ to foraging Antarctic fur seals
and found good correlation between seasonal
averages of fur seal IPQs and independent
acoustic assessments of krill abundance. They
also found that measured IPQ conformed well with
some intuitive expectations IPQ declined during
foraging bouts consistent with prey depletion or
dispersion in response to foraging, and reached
similar bout-ending values when fur seals
should abandon a patch and search for better
patches, consistent with optimal foraging theory.
This approach has potential utility in
assessment of critical habitat for endangered
Steller sea lions. Survival of juvenile sea lions
is believed to be a critical element in the
decline of the western stock, as well as to their
recovery. Direct measurement of prey availability
and foraging success over this important part of
their life history is difficult to impossible,
but an analytical tool that extracts information
about their foraging success using satellite
telemetry from instrumented animals could be
extremely valuable for identifying critical
seasons and areas where habitat protection (e.g.,
fishing restrictions) might enhance foraging
success for juvenile sea lions. Objectives Our
objective was to evaluate whether Mori and Boyds
IPQ metric could be usefully applied to satellite
telemetry data from juvenile Steller sea lions
and aid in identifying potentially critical
habitat. Such telemetry imposes certain
constraints relative to the TDR data used thus
far for estimating IPQ, but might allow temporal
and spatial patterns to be discovered. In
particular we were interested in whether IPQ, and
its associated metric E (net rate of energy gain
during diving) produced sufficient variation, and
spatial or temporal patterns that might indicate
important feeding areas for juvenile Steller sea
lions. Results are preliminary.

• Discussion
• The seasonal pattern matches earlier
  conclusions for average dive depth and bottom
  time, raising the possibility that the IPQ and
  predicted E either are not capturing new
  information about habitat quality, or result from
  an artifact in calculation. There is some
  empirical support for the theoretical conclusion
  that patches of equal quality should provoke a
  longer bottom time during deeper dives. The IPQ
  measure accommodates that prediction, so our
  result suggests either that it does not
  compensate enough for that effect when sea lions
  follow a shift in prey depths in winter, or that
  Steller sea lions forage deeper in winter because
  patch quality and foraging success improves at
  deeper depths.
• Mean IPQ in a much-used area N of Glacier Island
  in winter (below) was only slightly above
  average. In this shallow area, an overestimate of
  surface interval could lead to an underestimate
  in the calculated IPQ (see central box).
• Much more needs to be done to understand and
  improve on the IPQ. This includes theoretical
  questions about the dive duration to surface
  recovery function, and the influence of it and
  other assumptions on the IPQ. Any index to
  habitat quality derived from dive data will also
  require sophisticated field techniques to
  validate the measure against divers foraging in a
  known prey-field.

• Results
• afa

• Methods
• Data come from 12 yearling Steller sea lions
  instrumented with satellite-linked dive recorders
  (SLDRs) in Nov 2001 2003 and Mar 2005 in Prince
  William Sound, and one yearling near Kagalaska
  Island in Mar 2003. SLDRs provided duration and
  surface interval data from 99,890 dives, and
  time-depth profiles with 4 inflection points
  (Fedak et al. 2001) from 13,917 of these. Bottom
  time was defined as time spent at 80 of maximum
  depth. Location was interpolated between Argos
  locations at sea.
• We derived a power function relationship between
  duration and surface interval based on the lower
  30th percentile of surface intervals in 34
  duration categories (13-488 s) for all
  individuals. This relationship captured features
  we expected a priori a moderate surface interval
  for durations under the theoretical aerobic dive
  limit (ADL130 s) for juvenile Steller sea lions,
  and increasing intervals past the ADL (Curve B,
  above). We calculated IPQ (Mori and Boyd 2004,
  explained above) and rate of net energy gain (E)
  that is maximized in the IPQ function for each
  dive over 15 m and 10 s bottom time. We assumed
  the allometric field metabolic rate for marine
  mammals reported by Williams et al (2005), which
  was consistent with the energetic models of
  Winship et al. (2002) for yearling Steller sea
  lions. Temporal pattern was modeled with
  polynomial regression in BUGS with independent
  intercept values for each sea lion. The
  intercepts were used to rescale IPQs before
  plotting their locations in ArcView and obtaining
  average values within grid squares.

• Results
• Mean IPQ in yearling sea lions was 0.32 (range
  0.29-0.36), but varied as a 3rd order polynomial
  from Nov-July (Fig 1, fitted value in red).
• Predicted net rate of energy intake (E) during
  dives followed the same pattern, peaking in
  Nov-Jan and reaching a nadir in Apr-June (Fig 2).
  
• The mean IPQ among dives grouped by grid squares
  in Prince William Sound showed above-average
  values in the area most used (Fig top-right) in
  winter N of Glacier Island.
• In spring, mean IPQ was not associated with any
  clear pattern of dive locations, although three
  the 25 km2 blocks near the main haul-out for N
  Prince William Sound had the lowest calculated
  IPQs.

Acknowledgments We wish to thank the Steller sea
lion research program at Alaska Department of
Fish and Game for field support of this project.
Mike Rehberg (ADFG) and George Esslinger (USGS)
assisted with GIS analyses.
References Fedak et al. 2001. Two approaches to
compressing and interpreting time-depth
information as collected by time-depth recorders
and satellite-linked data recorders. Mar.Mamm.
Sci. 17 94-110. Mori, Y., et al. 2002. An
application of optimal diving models to diving
behaviour in Brünnichs guillemots. Animal
Behaviour 64 737-743. Mori, Y. and I.L. Boyd.
2004. The behavioral basis for nonlinear
functional responses and optimal foraging in
Antarctic fur seals. Ecology 85
398-410. Williams, T.M. et al. 2004. Killer
appetites assessing the role of predators in
ecological communities. Ecology
853373-3384. Winship, A.J. 2002. A bioenergetic
model for estimating the food requirements of
Steller sea lions Eumetopias jubatus in Alaska.
Marine Ecology Progress Ser. 229 291-312.