FISHERIES MANAGEMENT AND THE ROLE OF

APEX PREDATORS

Earth From Space

Satellite Image of North Central Gulf of Mexico

TXLA

MS AL

FL

Tan areas reflect continental shelf of Northern Gulf of Mexico

shelf

shelf

shelf

• Gulf of Mexico: a large marine ecosystem (LME)

• An ecosystem: “the complex of a community of organisms and its environment functioning as an ecological unit”

• How do we understand an ecosystem? Link (2002)

Ecosystem based fisheries management

Images from Large Marine Ecosystem project, Sherman et al.

Link J. 2002. Does food web theory work for marine ecosystems? Marine Ecology Progress Series 230: 1-9.

Red Drum or redfish were nearly depletedIn the 1980’s

Graduate student Matt Kenworthy studies red drum

APEX PREDATORS IN THE NORTHERN GULF OF MEXICO

Food Pyramid forthe Oceans

DIATOMS - Plants of the ocean

Copepods

Anchovy-Sardines

Cow

s of

the

ocea

n

Tunas and Mackerel

Wol

f of t

he o

cean

Sharks

APEX or Top Predator

9 8 9 6 9 4 9 2 9 0 8 8 8 6 8 4 8 22 4

2 6

2 8

3 0 Texas

LouisannaMississippi

Alabama

Florida

US Exclusive Economic Zone (EEZ)

1200 m isobath

NMFS Bottom Longline

• Fishery independent bottom longline database: 1995

• Gulf wide random site selection out to 400 meters

9 6 9 4 9 2 9 0 8 8 8 6 8 4 8 22 4

2 6

2 8

3 0

Blacktip shark Carcharhinus limbatus

8 9 8 8 8 72 9

3 0

3 1

1 2 3 4

M i s s i s s i p p i F l o r i d a

1 0 M 2 0 M

M o b i l e B a y

Blocks 1,2 West of Mobile BayBlock 3, 4, East of Mobile BayBlue Line -North South Transect

8 9 8 8 . 5 8 8 8 7 . 5 8 72 9

2 9 . 5

3 0

3 0 . 5

3 1

M S F L

M o b i l e B a y

2 0 m

2 0 0 m

2009 Survey

Blacktip SharkBlacktip Shark

Torpedo shaped for speedTorpedo shaped for speedCamouflaged top and bottomCamouflaged top and bottomAmpullae of Lroenzini-electric fieldsAmpullae of Lroenzini-electric fields1/3 to 2/3 of brain devoted to smell1/3 to 2/3 of brain devoted to smellMirror like reflective membrane toMirror like reflective membrane toenhance light gatheringenhance light gathering

Teeth are modified scalesTeeth are modified scales

Long-line

Buoy

Shark Bait

Hooks

Long-line gangets with baited hooks

Retrieving long-line with Shark

Hammerhead Shark

Sharks are brought on board to collect data

Tag has a number that corresponds to a data sheet and statement that says REWARDwith phone number

Tagging Shark

Tag

Species Identification, Sex and Weight

Tetracycline is injected as a marker

Tag

Marcus Dryman with Blacknose shark

Not all sharks survive beingcaught on the long-line, many Samples from stomach to livertissue are taken for further analysis

Atlantic Sharpnose sharks have a low tolerance for oxygen deprivation

Atlantic Sharpnose embryonic sharks, 4 in each uterus - 8 total

Southern Stingray

Circle hooks cause lessmortality

Red Drum are often caught on the long-line

Rarely sea turtle like this Loggerhead are fouled hooked on long-line

Nurse shark – hook being cut off to release shark

Juvenile Tiger sharkcaught ¼ mile off Alabama-Florida line

Tiger shark tagged and released

DISL

Satellite Tags

Acoustic Tagging

Gulp!

We Are the Top Predators

Even sea birds fall prey to sharks APEX predator – means being on the top of the food chain

Explosion and sinking of oil wellDeep Horizon

http://www.disl.orghttp://www.cosee-gom.org

References That You Can Review

Current-Journal of Marine Education Vol. 18 Number 1 2002

Harden, G. 1968. “The Tragedy of the Commons” Science 162:1243-1248

Husted, R., and R. Lent. “International Aspects of Atlantic Highly Migratory Species Management”. Current 14:22-24

Richards, W.J. & Edwards, R.E. (1986) “Stocking To Restore of Enhance Marine Fisheries” In : Fish Culture in Fisheries Management pp.75-80 American Fisheries Society

Web sites: www.ifmt.nf.ca/mi-net/fishdeve/index www.ncdmf.net www.nmfs.noaa.gov/sfa/magact www.vims.edu/bridge/archive0100 www.vims.edu/bridge/archive0299