The Effect of Fishing on Species and Genetic Diversity

• Genetic resources are an important element of conservation– Species– Within Species

I. The Loss of Species

• Is this a problem in the sea?• How do we know?

Latimeria chalumnae (coelacanth) c. 1938

Documented Extinction

• Steller’s Sea Cow• Caribbean Monk Seal• Eelgrass Limpet• Rocky Shore Limpet• Asian Periwinkle• Horn Snail

• New Zealand Grayling• Sea Mink• Great Auk• Vanvoorstia

bennettiana (Australian red alga)

Sea Turtles, Sharks, Rays ...

The Role of Fishing in Extinction Events

II. Loss of Populations

Pacific Salmonids

• Population rich– 106 populations extirpated in US– 142 populations extirpated in Canada– In the last 30 yrs over 40% of range lost

4VsW September/October 1996 longline survey catches

46

4363 57

Marine fish have much more genetic structure than previously supposed

Maintenance of Genetic Diversity

• Organization of populations in time and space

• Ratio of within and among population variation

Events Prior to Extinction

• Extirpation– Range contraction– Fragmentation

• Adriatic Sea stock of Beluga Sturgeon• Atlantic Ocean population of Gray Whale• Gulf of St. Lawrence walrus

– populations of 82 species of marine fish in North America believed to be at risk

Brosme brosme (cusk) Abundance 1970-2000

Loss of Populations = Loss of Genetic Diversity

-60 -55 -50 -45 -4042

44

46

48

50

52

54

56

2J

3K

3M

3N

3O

3L

196419781990's

Newfoundland

Labrador

NE Newfoundland Shelf

The Grand Bank

Flemish Cap

• A significant amount of genetic diversity could be attributed to spatial structure • No variance component could be attributed to temporal changes

Ruzzante, Taggart et al. In Press. Stability in the historical pattern of genetic structure of Newfoundland cod (Gadus morhua) despite the catastrophic decline in population size from 1964 to 1994. Conservation Genetics

III. Loss of within population genetic diversity

Selective Fishing

25

35

45

55

65

Size

at a

ge (c

m)

1970 1975 1980 1985 1990 1995

age 3

age 5

age 7

0

50

100

150

0

10

20

30

Num

ber

per

tow

(all

size

s)

Adul

t num

ber

per t

ow

1970 1975 1980 1985 1990 1995 2000

adult all sizes

• By removing the large fish selectively over time the remaining fish are slow-growing and early-maturing

• Genetic or Ecological?– temperature– abundance of prey– degree of competition

Traits affected by fishing?

• Weight-at-age• Length-at-age• Age-at-maturity• Length-at-maturity• Spawning season• Number and size of eggs

Selective fishing can cause heritable differences in

life-history traits that control sustainable yield

Problems and Solutions

• Species extinction

• Genetic complexity

• Selective fishing

• Address at the population level

• Manage spawning components

• Reduce fishing intensity• Structure effort• Reduce selectivity• Reduce fishing intensity

Numbers are not enough