-â40 towed by the R/V Henry B. Bigelow during the NOAA/ ... Bigelow â stra2fied random sampling, nearshore and offshore .... Dan Zapf. Jacob Boyd. Jeff Dobbs.
Diet Varia)on and Predatory Impact of Spiny Dogfish (Squalus acanthias) in North Carolina Waters Charles Bangley and Roger A. Rulifson Ins)tute for Coastal Science and Policy, Flanagan 385, East Carolina University, Greenville, NC
Introduc)on – Dogfish Feeding Ecology and Fisheries ATer crash of cod stocks, spiny dogfish became the dominant piscivore in the Northwest Atlan)c (Link and Garrison 2002). Strong preference for pelagic prey (Link et al. 2002) Occupy same feeding guild as many commercially important species in NW Atlan)c (Garrison and Link 2000)
Andy Murch – elsamodiver.com
Require annual food intake of 1.5 x body weight (BreZ and Blackburn 1978) or 2.5 x body weight (Jones and Geen 1977)
From Link et al. (2002)
Research Ques)ons Do environmental differences by size and sex affect the feeding habits of spiny dogfish? Do spiny dogfish consume or compete with other economically important piscivores? What are the effects? How do the ecological interac)ons between overwintering dogfish, their prey, and other predators affect North Carolina fisheries?
Andy Murch – elasmodiver.com
Methods – Sampling Sta)ons 240 sta)ons total -‐200 towed by the R/V Cape Ha1eras during the USFWS-‐led Coopera)ve Winter Tagging Cruise – Feb 18th-‐24th -‐40 towed by the R/V Henry B. Bigelow during the NOAA/NMFS spring boZom trawl survey – March 4th-‐8th Cape Ha1eras – specifically targeted striped bass, sta)ons chosen accordingly, nearshore sta)ons north of Cape HaZeras, 10-‐30 min tows Bigelow – stra)fied random sampling, nearshore and offshore sta)ons, some sta)ons south of Cape HaZeras, 20 min tows
Methods –Sampling Protocol Depth (m), water temperature (°C), and salinity (ppm), recorded at each sta)on. 10-‐15 dogfish (approx. one basket) of each sex randomly selected from each tow Stomach contents sampled from 399 dogfish total 253 from the Cape Ha1eras, 146 from the Bigelow Total length, fork length (mm) and sex recorded for each sampled dogfish Prey items iden)fied to lowest possible taxa, some specimens preserved in 70% ethanol for later iden)fica)on – hard parts (bones, scales, shells) used for ID of less intact prey
Methods – Analysis Prey taxa grouped into broad categories (Teleost, Elasmobranch, Crustacean, Mollusk, Other Invertebrate, Uniden)fied) for analysis Number, weight (g) recorded for each prey taxa and category, total length (mm) recorded for whole animals – used to calculate Index of Rela)ve Importance (% IRI) Consump)on es)mate for prey i:
Ci = R(S) * %Wi
Ci = biomass of prey i consumed R = annual ra)on (1.5 or 2.5) S = dogfish popula)on biomass %Wi = % weight of prey i Daily and monthly consump)on calculated Compared to landings and stock biomass data Calculated for 100%, 75%, 50%, 25% of dogfish biomass
Results – Overall Diet Cape Ha1eras % Weight, N = 7949.12 g 0.40% 0.43% 0.65% 1.29% 0.00% 0.35%
% IRI 0.48%
Teleost Elasmobranch
2.73%
Mollusk
94.16%
Crustacean
Teleost
Ctenophore
Other
Other Invert
99.52%
Uniden)fied Other
Bigelow % Weight, N = 993.38 g 2.06%
0.52% Teleost
Mollusk
4.82%
Crustacean
5.18% 60.85%
0.36% 0.14% 7.93%
2.53%
Teleost Elasmobranch
9.14%
Mollusk
0.01%
Crustacean
Ctenophore Other Invert
1.49%
0.70%
Elasmobranch
13.91%
11.17%
% IRI
Ctenophore 79.19%
Other Invert
Uniden)fied
Uniden)fied
Detritus
Detritus
Results – Bigelow Temperature Gradients Surface
BoZom
Results – Bigelow Salinity Gradients Surface
BoZom
Results – Bigelow Distribu)on by Sex Females
Males
Results – Bigelow Diet by Sex Females (n = 105) % Weight 2.05%
% IRI
5.45%
4.85% 0.53%
59.94%
1.53%
Ctenophore
11.43%
Detritus
14.23%
6.78% 0.51% 0.12% 0.01% 2.75%
0.28%
Crustacean
8.54%
Crustacean Ctenophore Detritus
Elasmobranch
Elasmobranch
Mollusc
Mollusc 81.01%
Other Invert
Other Invert
Teleost
Teleost
Males (n = 16) % IRI
% Weight 2.41% 10.36%
14.78%
2.94% 0.00%
Crustacean Ctenophore
1.60% Crustacean
0.31%
Ctenophore
3.44%
Detritus
Detritus Teleost 84.29%
Uniden)fied
79.88%
Teleost Uniden)fied
Results – Size, Environment, Feeding Mean Temperature (°C)
Mean Depth (m)
0 -‐50 -‐100 -‐150 -‐200 -‐250
12 10 8 6
Surface
4
BoZom
2 0
-‐300 Size Range (mm)
35 34.5 34 33.5 33 32.5 32 31.5 31
Surface BoZom
Size Range (mm)
IRI (Prey Category)
Mean Sallinity (ppm)
Size Range (mm)
100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%
Ctenophore Mollusc Other Invert Crustacean Teleost
TL range (mm)
Results – Bigelow Environmental Demographics Females Depth – Surface Temp – BoZom Temp – Surface Salinity – BoZom Salinity –
Males
54.02 m 185.70 m 5.76 °C 7.30 °C 7.13 °C 9.11 °C 32.99 ppm 34.21 ppm 33.64 ppm 34.64 ppm
All differences significant at α = 0.05 > 650 mm ≤ 650 mm Depth – 70.70 m 196.80 m Surface Temp – 5.96 °C 7.41 °C BoZom Temp – 7.44 °C 8.59 °C Surface Salinity – 33.18 ppm 33.73 ppm BoZom Salinity – 33.80 ppm 34.36 ppm Andy Murch – elasmodiver.com
Depth, surface temp, and boZom salinity differences significant at α = 0.05
Results – February and March Consump)on Spiny dogfish biomass = 360,040 mt (Rago and Sosebee 2010) Annual food intake = 541,560 mt at 1.5 x bw, 902,600 at 2.5 x bw % dogfish biomass
Total Feb/Mar consumption (mt)
% landings (NMFS 2010)
Atlantic croaker
100% 75% 50% 25%
1066.30 799.73 533.15 266.58
14.68% 11.01% 7.34% 3.67%
Squid
100% 75% 50% 25%
4512.51 3384.38 2256.25 1128.13
14.97% 11.23% 7.49% 3.74%
Bay anchovy
100% 75% 50% 25%
16322.72 12242.04 8161.36 4080.68
-
Ctenophore
100% 75% 50% 25%
68146.30 51109.73 34073.15 17036.58
-
Results – February Consump)on Menhaden most important prey item in February (57.33% IRI, 59.82% W) Present in March only as well-‐digested remains (0.97% IRI, 1.19% W) 14% within size range of spawning stock (age 3+) Striped bass rela)vely unimportant in diet, but of economic concern % dogfish biomass Atlantic Menhaden
Striped Bass
February consumption % landings (mt) (NMFS 2010)
% biomass*
100% 75% 50% 25%
41419.70 31064.77 20709.85 10354.92
22.73% 17.05% 11.37% 5.68%
5.80% 4.35% 2.90% 1.45%
100% 75% 50% 25%
1592.53 1194.40 796.27 398.13
9.58% 7.19% 4.79% 2.40%
1.47% 1.10% 0.74% 0.37%
*Menhaden = SSB (age 3+) (ASMFC 2011), striped bass = pop. biomass (ASMFC 2009)
Results – Prey/Predator Size Rela)onships Overall Prey Prey TL (mm)
500
y = 0.5287x -‐ 336.96 R² = 0.21154
400 300
Overall Prey
200 100 0 400
Linear (Overall Prey) 600
800
Bi)ng allows mature dogfish to overcome gape limita)on
Prey/Shark raEo % dogfish TL
0.5
y = 0.0005x -‐ 0.2844 R² = 0.14184
0.4 0.3
Prey/Shark ra)o
0.2 Linear (Prey/Shark ra)o)
0.1 600
800
Dogfish TL (mm)
Menhaden were largest common prey
1000
Dogfish TL (mm)
0 400
Prey TL and ra)o of prey/ predator TL both correlate significantly with dogfish TL (α = 0.05)
1000
TL of two striped bass es)mated by ageing scales: Age 12 = 850 mm TL, 108% and 113% of predator TL
Conclusions Diet and habitat use related to size and sex – large females occupy nearshore waters and consume mostly fish Diverse piscivorous diet – mainly small forage species and juveniles but capable of consuming large prey Menhaden consump)on in Feb may be ecologically significant Direct preda)on not a large source of mortality for striped bass, but poten)al for indirect effects
Andy Murch – elasmodiver.com
Acknowledgements Thesis CommiFee Dr. Roger A. Rulifson (Chair, East Carolina University) Dr. Anthony Overton (East Carolina University) Dr. Patrick Harris (East Carolina University) Dr. Brad Wetherbee (University of Rhode Island) Rulifson Lab Jennifer Cudney-‐Burch Coley Hughes Dan Zapf Jacob Boyd Jeff Dobbs Garry Wright American Fisheries Society American Elasmobranch Society ECU Biology Graduate Student AssociaEon The crew of the Cape Ha'eras and Henry B. Bigelow
Ques)ons?
Andy Murch – elasmodiver.com
