Using the otolith sulcus to aid in prey identification and improve estimates of prey size in diet studies of a piscivorous predator

Description

Diet studies are fundamental for understanding trophic connections in marine ecosystems. In the southeastern US, the common bottlenose dolphin Tursiops truncatus is the predominant marine mammal in coastal waters, but its role as a top predator has received little attention. Diet studies of piscivorous predators, like bottlenose dolphins, start with assessing prey otoliths recovered from stomachs or feces, but digestive erosion hampers species identification and underestimates fish weight (FW). To compensate, FW is often estimated from the least affected otoliths and scaled to other otoliths, which also introduces bias. The ulcus, an otolith surface feature, has a species-specific shape of its ostium and caudal extents, which is within the otolith edge for some species. We explored whether the sulcus could improve species identification and estimation of prey size using a case study of four sciaenid species targeted by fisheries and bottlenose dolphins in North Carolina. Methods were assessed first on otoliths from a reference collection (n=421) and applied to prey otoliths (n=5308) recovered from 20 stomachs of dead stranded dolphins. We demonstrated in reference collection otoliths that cauda to sulcus length (CL:SL) could discriminate between spotted seatrout (Cynoscion nebulosus) and weakfish (Cynoscion regalis) (classification accuracy=0.98). This method confirmed for the first time predation of spotted seatrout by bottlenose dolphins in North Carolina. Using predictive models developed from reference collection otoliths, we provided evidence that digestion affects otolith length more than sulcus or cauda length, making the latter better predictors. Lastly, we explored scenarios of calculating total consumed biomass across degrees of digestion. A suggested approach was for the least digested otoliths to be scaled to other otoliths iteratively from within the same stomach, month, or season as samples allow. Using the otolith sulcus helped overcome challenges of species identification and fish-size estimation, indicating their potential use in other diet studies.

Resources

Name Format Description Link
57 58439.zip https://grunt.sefsc.noaa.gov/parr/58439.zip
0 View the complete metadata record on InPort for more information about this dataset. https://www.fisheries.noaa.gov/inport/item/58439
0 Website listed for Hohn, Aleta https://scholar.google.com/citations?user=wd1SXSQAAAAJ
33 NOAA Data Management Plan for this record on InPort. https://www.fisheries.noaa.gov/inportserve/waf/noaa/nmfs/sefsc/dmp/pdf/58439.pdf
0 The information provided on this page seeks to define how the GCMD Keywords are structured, used and accessed. It also provides information on how users can participate in the further development of the keywords. https://www.earthdata.nasa.gov/learn/find-data/idn/gcmd-keywords

Tags

  • stomach contents - digestion
  • common bottlenose dolphin
  • biological data
  • stomach contents - content weight
  • protected resources marine mammals (beaufort)
  • stomach contents - prey taxonomy
  • 1996-2012
  • noaa
  • southeast fisheries science center
  • doc/noaa/nmfs/sefsc
  • in situ
  • fish examination
  • u.s. department of commerce
  • national marine fisheries service
  • tursiops
  • coastal waters of north carolina
  • biological
  • stomach contents - fullness
  • stomach contents - prey count
  • animals - individual - stomach contents
  • laboratory analyses
  • north atlantic ocean

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