Salmon age and size at maturity: Patterns and processes

Transcription

1 Salmon age and size at maturity: Patterns and processes 1. Age Designation 2. Variation among populations 1. Latitude 2. Within regions 3. Within watersheds 3. Variation within populations 1. Smolt size 2. Growth rate 3. Non-anadromy 4. Size Sex Ratio 5. Catch vs. Spawning Population 6. Declines in Size and/or Age

2 Age Designation The total age of the fish does not capture important life history events. Rather, we need to indicate the periods of time spent in freshwater and at sea to distinguish fish of the same age with different life histories. In addition, we need a way to account for the period of time spent as a developing embryo and alevin. There are two distinctly different but equivalent ways in which salmon ages are commonly designated (plus a third used in Russia).

3 Age Designations: for example, Years spent Freshwater Saltwater a sockeye salmon U.S. (European) Designation Canadian (Gilbert-Rich) Total Age N.B. These years are really winters as a free-swimming fish. This includes the missing year in embryonic stages

4 Age Designations Years spent Freshwater Saltwater U.S. (European) Designation Canadian (Gilbert-Rich) Total Age

5 Age Designations Years spent Freshwater Saltwater U.S. (European) Designation Canadian (Gilbert-Rich) Total Age

6 Age Designations Years spent Freshwater Saltwater U.S. (European) Designation Canadian (Gilbert-Rich) Total Age

7 Age Designations Years spent Freshwater Saltwater U.S. (European) Designation Canadian (Gilbert-Rich) Total Age

8 Features used for Age Determination: 1. Otoliths (ear bones): Record information during embryonic stages, permanent, but necessitate lethal or post-mortem sampling 2. Scales: not deposited until some period of growth has taken place, can fall off and get replaced, but can be removed from live fish Aside: Otoliths are mineral and generally yield no DNA but scales can yield DNA from decades past, before DNA was discovered.

9 Age 1.2 sockeye salmon, Bristol Bay Second marine check at the edge focus Freshwater check First marine check

10 SW 3 SW 2 SW 1 FW 1 Age 1.3 Bristol Bay sockeye salmon

11 Age 4 steelhead from Forks Creek: Michael Dauer 2 nd winter in SW 1 st winter in SW 2 nd winter in FW Scale focus 1 st winter in FW

12 Returned in 2002 Spawned in 2001 Smolted in 1998 Emerged in 1997 Winter of 2000 at sea Winter of 1999 at sea Repeat spawning hatchery steelhead from Forks Creek: Michael Dauer

13 Returned in 1998 Returned in 1997 Wild steelhead: three time spawner Winter 1994 in fresh water Returned in 1996 Emerged in 1992 Winter 1995 at sea Winter 1993 in fresh water

14 For steelhead and other iteroparous species, the age designation must indicate spawning events as well as the years spent in freshwater and at sea. Michael Parker A 4-year old fish on its first return might be a 1.3 if it went to sea at age 1 but a fish of the same age that spawned in the previous year would be designated 1.1S1. Repeat spawners are smaller than maidens of the same age.

15 Distribution of sockeye salmon by total age in the Chignik Lake system, AK % of run Dahlberg (1968) Total Age

16 Distribution of Chignik Lake system sockeye salmon by age group Mean % of run jacks Age Group

17 Hypothesized costs in mortality and benefits in fecundity of marine residence 1.0 Ocean age 1 Survival to spawning Fecundity 5000 Proportion surviving to spawn Ocean age 2 Ocean age Fecundity Ocean age Fork length (mm)

18 Overall length varies greatly among populations: Mean lengths of North American Chinook salmon populations Number of populations males females Roni 1992 Post-orbit to hypural length (mm)

19 Kitsumkalum River chinook salmon

20 Levels of variation in age and size at maturity among populations Latitude Regional features Local features

21 Are all the big salmon are in Alaska? Not necessarily. Examination of Chinook salmon did not yield any clear trend of size with latitude once age had been accounted for. Coho salmon seem to be larger in Alaska but this does not seem to have been documented, and pink and chum are often smaller in Alaska than farther south, at a given age. Roni 1992 Puget Sound, ca. 50 cm)

22 Pink salmon weight and chum salmon length (e.g., age-4) decreases with latitude Pink salmon weight (kg) Arctic Bristol Bay Alaska Peninsula Kodiak Prince William Sound pink weight chum length SE Alaska N British Columbia S British Columbia Fraser River Washington Oregon Chum salmon length (mm)

23 The area where salmon enter the ocean has little effect on their final body size. Small-bodied populations may be located near large-bodied ones, so the differences in size must be related to other things.

24 Iliamna Lake Fishing districts Wood River Kvichak River Togiak Nushagak Naknek- Kvichak Naknek River Egegik Bristol Bay Ugashik

25 Sockeye salmon ocean age varies among districts within Bristol Bay, and among river systems within districts Ocean age (%) District System 2 3 Naknek-Kvichak Alagnak Kvichak Naknek total Nushagak Igushik Nushagak Wood total 42 58

26 Older and larger fish tend to predominate in larger rivers (e.g., Wood River sockeye) but they have access to the same growing conditions % ocean-age 3 salmon Stream width (m) in the Wood River system 1.8 A and C creeks 3.8 Hansen Creek Bear Creek Ice Creek Agulowak River

27 Some individuals and populations tend to grow faster than others. In addition, individuals and populations differ in the norm of reaction between growth and maturation. That is, growing at the same rate, some will mature in the next year whereas others with stay at sea, grow larger, and mature at an older age. Really big fish are not faster growing.

28 Male chinook salmon Age 4 Age 1

29 What controls age at maturity within populations? Growth in freshwater or smolt size Growth at sea Genetics Coho smolt Chinook

30 Back-calculated lengths of Chinook salmon (in mm) at different ages, as a function of their final age at maturity (data from Parker and Larkin 1959). Age at maturity AGE Sample

31 Lengths of Asian chum salmon sampled at sea that were maturing or immature at successive ages. Maturing fish were consistently larger than the immature fish of their age. Fork length (mm) LaLanne 1971 immature maturing May 1-May 1-May 1-May

32 Not only growth rate at sea but smolt size affects age at maturity. Fish that mature at an early age generally were older/larger as smolts (e.g., Wood River sockeye salmon). % of each marine age group Age-1 smolts Age-2 smolts Number of years spent at sea before returning

33 Mature male UW Chinook salmon Age 1 Age 2 Age 3 Age 4

34 Average smolt weight affected the percent of male UW Chinook that matured as jacks and especially age-1 mini-jacks age 1 jacks all jacks 70 % of males Average smolt weight (g)

35 The tendency of female UW Chinook to mature at age 3 rather than age 4 was also related to average smolt weight 100 % age 3 females Average smolt weight (g)

36 Size, sex and survival In most populations, the sex ratio is nearly 50:50, and males are slightly larger for their age than females (Why?) In many coho salmon populations, males outnumber females but are smaller So, do females incur a higher mortality associated with their larger size? And why are females larger than males in coho, but smaller in sockeye salmon, for example? N.B. Fishing rate on jacks is low, so surveys in streams inflate their apparent abundance.

37 Is there also a genetic control over age at maturity? Insert photo of adult coho and jack Do jacks beget jacks?

38 Females mated with jack Chinook salmon produced more jacks and fewer old males than females mated with older males % of adult offspring Hankin et al Sired by jacks Age at maturity of males Sired by older males 2 x x 4+

39 Genetic control over age at return in steelhead Ocean age of parents Ocean age of offspring (%) Tipping 1991

40 Fisheries can be selective with respect to size, and thus age (e.g., Nushagak River female sockeye in 1984) 1 Proportion caught or escaping Escaped Caught Length

41 Further complexities There may be non-anadromous individuals (typically males) in anadromous populations Variation in size within non-anadromous populations related to food resources, selection from physical habitat limitation, predation risk, etc.

42 Cedar River 1 + Chinook salmon smolt Cedar River precocious male Chinook salmon

43 Large-bodied rainbow trout from British Columbia

44 Resident cutthroat trout

45 Genetic and Environmental Factors Influencing Age and Size at Maturity Age at Maturity: Primarily represents a trade-off between the reproductive benefits of increased size against the risk of mortality in the next year. Age at maturity is negatively related to growth rate or size at age. Size at Age: Results from 1) natural selection from factors associated with reproductive success, predation, and physical features of the migratory route and spawning grounds, and 2) environmental influences on growth rate.

46 Declines in size or age at maturity have been recorded in many populations Average Length (mm) UW female coho salmon r 2 =

47 Possible reasons for declines in size and age at maturity (Ricker 1980) 1. Biased data 1. Fish caught earlier in the season 2. Fish caught in the year prior to maturity 2. Genetic changes 1. Selective loss of large-bodied populations 2. Fishing selects for fish that mature early in life 3. Size selective fishing selects for small/young fish 3. Environmental changes 1. Changes in temperature affect growth and maturation 2. Changes in density affect growth and maturation 4. Effects of hatcheries 1. Large smolts mature at an earlier age than small ones 2. Selection for large fish actually selects for slow growth