Species and size differences in the digestion of otoliths and beaks: Implications for estimates of pinniped diet composition

D J  Tollit; M J  Steward; P M  Thompson; Graham John Pierce; M B  Santos; S  Hughes

Species and size differences in the digestion of otoliths and beaks: Implications for estimates of pinniped diet composition

D J Tollit, M J Steward, P M Thompson, Graham John Pierce, M B Santos, S Hughes

Research output: Contribution to journal › Article › peer-review

Abstract

We examined the digestion of hard remains of between one and four different size ranges of nine key North Sea prey taxa fed to seven captive harbour seals (Phoca vitulina). Percentage length reduction (mean 27.5%) and recovery rates (mean 42%) of experimental otoliths varied between species and were positively correlated to fish size and otolith robustness (mass/length). Mean length reduction of egested otoliths increased systematically with increasing size of ingested whiting and sandeel otoliths (p < 0.001), indicating that the size of larger fish may be underestimated. Intraspecific variation in otolith digestion was high (CV = 0.48-1.30), and to control for the artificial conditions of a captive study, external morphological features of otoliths were used to grade the degree of digestion and provide grade-specific correction factors. Bootstrap simulations were used to estimate 95% confidence intervals around correction factors and when partitioned indicated that calculation errors were in general less important than resampling errors. The application of species-, size-, and grade-specific correction factors progressively improved reconstructed estimates of prey biomass fed. As a consequence, estimates of prey size and diet composition require otoliths from faeces to be graded and more complex correction factors applied.

Original language	English
Pages (from-to)	105-119
Number of pages	15
Journal	Canadian Journal of Fisheries and Aquatic Sciences
Volume	54
Issue number	1
Publication status	Published - Jan 1997

Bibliographical note

We thank all the staff at the Sea Life Centre and Bruce Greig for their assistance. We thank Don Bowen, Heather Corpe, Simon Greenstreet, Kate Grellier, Ailsa Hall, Phil Hammond, John Hislop, Paul Racey, David Rosen, Phil Smith, Ben Wilson, and an anonymous reviewer for constructive criticism to 116 Can. J. Fish. Aquat. Sci. Vol. 54, 1997 © 1997 NRC Canada
earlier manuscripts. Thanks also to everyone at the Lighthouse Field Station for advice and encouragement. The majority of the work was carried out under a series of contracts from the
Scottish Office Agriculture and Fisheries Department to Professor P.A. Racey and P.M.T. G.J.P. was supported by a Commission of the European Community (CEC) contract (AIR 1 CT92 0573) and M.B.S. was supported by a CEC fellowship (ERB 4001 GT93 3630).

Keywords

seals phoca-vitulina
feeding-habits
harbor seals
gastric evacuation
Moray-Firth
grey seals
gray seals
North Sea
Scotland
prey

Cite this

@article{25cb94e595494f479b1c433ae7574266,

title = "Species and size differences in the digestion of otoliths and beaks: Implications for estimates of pinniped diet composition",

abstract = "We examined the digestion of hard remains of between one and four different size ranges of nine key North Sea prey taxa fed to seven captive harbour seals (Phoca vitulina). Percentage length reduction (mean 27.5%) and recovery rates (mean 42%) of experimental otoliths varied between species and were positively correlated to fish size and otolith robustness (mass/length). Mean length reduction of egested otoliths increased systematically with increasing size of ingested whiting and sandeel otoliths (p < 0.001), indicating that the size of larger fish may be underestimated. Intraspecific variation in otolith digestion was high (CV = 0.48-1.30), and to control for the artificial conditions of a captive study, external morphological features of otoliths were used to grade the degree of digestion and provide grade-specific correction factors. Bootstrap simulations were used to estimate 95% confidence intervals around correction factors and when partitioned indicated that calculation errors were in general less important than resampling errors. The application of species-, size-, and grade-specific correction factors progressively improved reconstructed estimates of prey biomass fed. As a consequence, estimates of prey size and diet composition require otoliths from faeces to be graded and more complex correction factors applied.",

keywords = "seals phoca-vitulina, feeding-habits, harbor seals, gastric evacuation, Moray-Firth, grey seals, gray seals, North Sea, Scotland, prey",

author = "Tollit, {D J} and Steward, {M J} and Thompson, {P M} and Pierce, {Graham John} and Santos, {M B} and S Hughes",

note = "We thank all the staff at the Sea Life Centre and Bruce Greig for their assistance. We thank Don Bowen, Heather Corpe, Simon Greenstreet, Kate Grellier, Ailsa Hall, Phil Hammond, John Hislop, Paul Racey, David Rosen, Phil Smith, Ben Wilson, and an anonymous reviewer for constructive criticism to 116 Can. J. Fish. Aquat. Sci. Vol. 54, 1997 {\textcopyright} 1997 NRC Canada earlier manuscripts. Thanks also to everyone at the Lighthouse Field Station for advice and encouragement. The majority of the work was carried out under a series of contracts from the Scottish Office Agriculture and Fisheries Department to Professor P.A. Racey and P.M.T. G.J.P. was supported by a Commission of the European Community (CEC) contract (AIR 1 CT92 0573) and M.B.S. was supported by a CEC fellowship (ERB 4001 GT93 3630).",

year = "1997",

month = jan,

language = "English",

volume = "54",

pages = "105--119",

journal = "Canadian Journal of Fisheries and Aquatic Sciences",

issn = "0706-652X",

publisher = "CANADIAN SCIENCE PUBLISHING, NRC RESEARCH PRESS",

number = "1",

}

TY - JOUR

T1 - Species and size differences in the digestion of otoliths and beaks

T2 - Implications for estimates of pinniped diet composition

AU - Tollit, D J

AU - Steward, M J

AU - Thompson, P M

AU - Pierce, Graham John

AU - Santos, M B

AU - Hughes, S

N1 - We thank all the staff at the Sea Life Centre and Bruce Greig for their assistance. We thank Don Bowen, Heather Corpe, Simon Greenstreet, Kate Grellier, Ailsa Hall, Phil Hammond, John Hislop, Paul Racey, David Rosen, Phil Smith, Ben Wilson, and an anonymous reviewer for constructive criticism to 116 Can. J. Fish. Aquat. Sci. Vol. 54, 1997 © 1997 NRC Canada earlier manuscripts. Thanks also to everyone at the Lighthouse Field Station for advice and encouragement. The majority of the work was carried out under a series of contracts from the Scottish Office Agriculture and Fisheries Department to Professor P.A. Racey and P.M.T. G.J.P. was supported by a Commission of the European Community (CEC) contract (AIR 1 CT92 0573) and M.B.S. was supported by a CEC fellowship (ERB 4001 GT93 3630).

PY - 1997/1

Y1 - 1997/1

N2 - We examined the digestion of hard remains of between one and four different size ranges of nine key North Sea prey taxa fed to seven captive harbour seals (Phoca vitulina). Percentage length reduction (mean 27.5%) and recovery rates (mean 42%) of experimental otoliths varied between species and were positively correlated to fish size and otolith robustness (mass/length). Mean length reduction of egested otoliths increased systematically with increasing size of ingested whiting and sandeel otoliths (p < 0.001), indicating that the size of larger fish may be underestimated. Intraspecific variation in otolith digestion was high (CV = 0.48-1.30), and to control for the artificial conditions of a captive study, external morphological features of otoliths were used to grade the degree of digestion and provide grade-specific correction factors. Bootstrap simulations were used to estimate 95% confidence intervals around correction factors and when partitioned indicated that calculation errors were in general less important than resampling errors. The application of species-, size-, and grade-specific correction factors progressively improved reconstructed estimates of prey biomass fed. As a consequence, estimates of prey size and diet composition require otoliths from faeces to be graded and more complex correction factors applied.

AB - We examined the digestion of hard remains of between one and four different size ranges of nine key North Sea prey taxa fed to seven captive harbour seals (Phoca vitulina). Percentage length reduction (mean 27.5%) and recovery rates (mean 42%) of experimental otoliths varied between species and were positively correlated to fish size and otolith robustness (mass/length). Mean length reduction of egested otoliths increased systematically with increasing size of ingested whiting and sandeel otoliths (p < 0.001), indicating that the size of larger fish may be underestimated. Intraspecific variation in otolith digestion was high (CV = 0.48-1.30), and to control for the artificial conditions of a captive study, external morphological features of otoliths were used to grade the degree of digestion and provide grade-specific correction factors. Bootstrap simulations were used to estimate 95% confidence intervals around correction factors and when partitioned indicated that calculation errors were in general less important than resampling errors. The application of species-, size-, and grade-specific correction factors progressively improved reconstructed estimates of prey biomass fed. As a consequence, estimates of prey size and diet composition require otoliths from faeces to be graded and more complex correction factors applied.

KW - seals phoca-vitulina

KW - feeding-habits

KW - harbor seals

KW - gastric evacuation

KW - Moray-Firth

KW - grey seals

KW - gray seals

KW - North Sea

KW - Scotland

KW - prey

M3 - Article

SN - 0706-652X

VL - 54

SP - 105

EP - 119

JO - Canadian Journal of Fisheries and Aquatic Sciences

JF - Canadian Journal of Fisheries and Aquatic Sciences

IS - 1

ER -

Species and size differences in the digestion of otoliths and beaks: Implications for estimates of pinniped diet composition

Abstract

Bibliographical note

Keywords

Fingerprint

Cite this