Homing migration of salmon on the open ocean

Transcription

1 Homing migration of salmon on the open ocean 1. Historical context 2. Techniques 3. Patterns for different species 4. Hypothesized mechanisms 5. Evidence of orientation

2 Historical context In 1927 Japan initiated mothership-based gillnet fisheries for salmon outside its territorial waters, in contrast to the policies of Russia, Canada and the USA to restrict fishing to the coastal zone. The Japanese fisheries expanded and in 1933 Japan initiated land-based gillnet fisheries as well. After World War 2, as Japan s economy rebounded, their fisheries expanded again, and concerns were expressed by US and Canada that North American salmon were being caught. The International North Pacific Fisheries Commission (INPFC) was formed, and Japan, Canada and the US conducted extensive research on the distribution, movements, and ecology of salmon at sea. The US research was among the focal programs of the Fisheries Research Institute, and it is still is conducted by University of Washington staff. The INPFC was reorganized to include Russia as the North Pacific Anadromous Fish Commission.

3 Methods for studying the migrations of salmon at sea Assess catch per unit of effort in different areas, using different types of gear. Determine direction of movement based on catch patterns. Assign fish to region or continent or origin based on variation in parasites, scale patterns, and (later) genetic techniques.

4 High seas research gillnet fishing

5 Research longline fishing

6 Research purse seining

7 Methods for studying the origin of salmon at sea Tag immature or maturing salmon at sea and recover them in coastal areas or rivers, assumed to be their origin

8 Methods for studying the origin of salmon at sea Tag juvenile salmon in freshwater and recover them at sea, defining the ocean range of that population 1 mm long Magnetized coded wire tag and a coho salmon smolt

9 Use of parasites to determine the origin of salmon If the parasite infests the salmon in freshwater, and if it has a limited geographical range, then infested salmon caught at sea must have come from that area. For example, northern pike are not found in the Asian range of sockeye salmon, nor in the North American range except in western Alaska (mainly Bristol Bay). A cestode parasite goes through sockeye salmon to pike, and so sockeye at sea with the parasite must have come from this region.

10 Migration: Definition and key elements Migration is a habitat change, undertaken by members of a population or species, coordinated in space and time. 1. Movement in space involves locomotion, which has active and passive components, and orientation, which includes tactic and kinetic responses, piloting, compass orientation, and navigation. 2. Coordination in time involves initiation and cessation. The animal responds to internal rhythms, synchronized by external stimuli.

11 Bering Sea Alaska North Pacific Ocean Gulf of Alaska B.C. Washington Oregon California

12 Typical migration patterns among species 1. Sockeye, chum, and pink salmon: Juveniles migrate northward along the continental shelf during their first summer at sea, then move to offshore waters until they mature. Relatively rapid homeward migration to coastal waters, often making landfall north of the river of origin. 2. Coho and chinook salmon: many juveniles occupy coastal waters north or south of their river of origin, and travel homeward more slowly than group (1), though some individuals or populations feed on the open ocean. 3. Steelhead: Migrate directly offshore to distant oceanic areas and migrate rapidly homeward at maturity. 4. Cutthroat trout, Dolly Varden, and Arctic charr: spend only a summer at sea, and do not go far from their river of origin (perhaps not true of Dolly Varden).

13 Indirect evidence of orientation at sea 1. Non-random movements of salmon at sea 2. Divergence of salmon from different populations experiencing common environmental conditions, to their respective home rivers 3. Convergence of salmon from a large area at sea, where individuals experienced different environmental conditions, to their home river 4. Travel rates of salmon at sea 5. Regularity in timing of arrival to coastal areas 6. Orientation abilities of juvenile salmon

14 Research fishing operations reveal that salmon at sea do not swim randomly

15 Divergence of sockeye from a purse seine set

16 Distribution of chum salmon caught at one area over a period of a month

17 Distribution of maturing Bristol Bay sockeye salmon, based on tagging and scale pattern analysis

18 Net travel rates of maturing sockeye salmon, based on tag-recapture data Migration rate (km/day) Bristol Bay Fraser River April May June July

19 Relationship between swimming speed and orientation required to travel 48 km/day 100% 70% 50% 10% 10% 20% 20% 10% 10% 2 km/h 3.3 km/h 5 km/h

20 Some populations arrive in coastal locations with precise timing Progression of sockeye salmon runs (escapement + catch) in Bristol Bay districts, averaged from Cumulative percent of the run District 10% 25% 50% 75% 90% Naknek-Kvichak 27-Jun 30-Jun 3-Jul 7-Jul 11-Jul Nushagak Nusagak 28-Jun 1-Jul 4-Jul 8-Jul 12-Jul Ugashik 2-Jul 4-Jul 8-Jul 11-Jul 15-Jul Egegik 26-Jun 1-Jul 3-Jul 7-Jul 11-Jul

21 Orientation abilities of juvenile salmon The migrations of juvenile sockeye salmon in large lakes seem to be guided by a sun compass, and also by a magnetic compass. If the fish are capable of such orientation in lakes, might they not be expected to use these sensory systems in the open ocean? Birds, sea turtles, and many other animals use such mechanisms to guide their migrations.

22 Migration in freshwater and at sea are guided by different clues and different sensory systems we believe olfaction to be singularly important to salmon migrating within a stream system but far less important to migration within the open sea. The factors which guide the salmon to the oceanic feeding ground and which guide its oriented return through the sea are indeed complex. Arthur Hasler Underwater Guideposts. Univ. of Wisconsin Press

23 Hypotheses regarding salmon orientation at sea 1. Random movement: little or no orientation capability is needed to explain the homeward movements (Saila and Shappy 1963) 2. Physiological optimization: fish migrations are explained, in large part, by the continuous optimization of physiological conditions such as temperature and salinity (Leggett 1977) 3. Map, compass and calendar: It thus becomes necessary to postulate that salmon have a bi-coordinate system of navigation that enables them to know where they are and where they are to go (and when to leave in order to get there on time). (Larkin 1975)

24 Locus (John Skapski) Salmon wind their tails, those obscure traces Marked on dog-eared charts Webbed in the organic circuitry Of fishermen s fading memories: Paths marked by numbers in tallybooks Statistics sargasso among blood tides Fins slice the surface of thought. Tails Steady into currents in past. Those routes Gauged only by numbers in nets, and we Were never everywhere at once. Or ever.

25 Fraser River sockeye approach the river via two routes

26 The percent of the Fraser River sockeye salmon run using Johnstone Strait (the northern route) varies considerably, and tends to be greater on years with warmer temperatures at sea in spring. % migrating via Johnstone Strait

27 The percent of Fraser River sockeye salmon using Johnstone Strait tends to be high when the run is late. Chilko River timing to Area 20 Median migration date 18-Aug 8-Aug 29-Jul 19-Jul % migrating through Johnstone Strait

28 Sockeye migrating to the Fraser River, at the southern end of their range, tend to be late after a warm spring whereas Bristol Bay sockeye, at the northern end of the range, tend to be early. Median migration date R 2 = Chilko River Median migration date R 2 = Bristol Bay May sea temperature deviation June sea temperature deviation

29 Blackbourn s hypothesis to explain year-to-year variation in timing and migratory route of sockeye

30 Migrations of Fraser River sockeye salmon Purpose: to collect descriptive information on the migration patterns of adult Fraser River sockeye salmon as a model for understanding the mechanisms guiding homeward migrations in complex coastal waters. Determine swimming speed, use of shorelines and open water, change in behavior with tides, vertical movements, diel activity patterns, and ways in which behavior differs between oceanographic regimes.

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32 Basic technique: catch a sockeye salmon and give it an ultrasonic transmitter.

33 Let the fish go, follow it, and record information on temperature, salinity and currents along the way.

34 Adult sockeye salmon movement directions Most sockeye moved SE, the direction of the Fraser River, some swam NW, the opposite direction, but few went NE or SW. 180 Home

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39 So, some salmon moved towards home, some moved in the opposite direction but, if followed long enough, often swung around towards the homeward direction. Is this to-and-fro pattern merely a result of fish drifting with the currents or were they actively swimming?

40 By using the speed and direction of the water current as a vector and the speed and direction of the fish s movement as the resultant, it was possible to estimate the actual speed and direction of the fish s swimming.

41 Estimated swimming speed of adult sockeye salmon, relative to the water Mean = 67 cm/s Frequency Swimming speed (cm/sec)

42 The water currents tend to run along the NW SE axis, because this is the general orientation of Vancouver Island and the mainland. Proportion of current drogues drifting in different compass directions

43 Even after vectoring out the effects of the currents, it is clear that some salmon swam in the opposite direction from home. Swimming directions of the sockeye salmon, relative to the water

44 Fishermen tend to fish near shore, and many expressed the belief that the salmon all migrate along the shorelines.

45 Seine sets in open water tended to catch a few salmon. Catches near shore (often in bays and coves) sometimes caught very many salmon. 75 % of seine hauls offshore onshore Sockeye salmon caught per haul

46 Pinball hypothesis We hypothesized that the salmon have a tendency to swim southeast, but if they encounter land they do not follow the shoreline. Rather, they reverse their direction, swim for a while in the opposite direction, then turn around and make another run at it. Given the complex shoreline, this is a more efficient strategy than following the shoreline. It would explain the presence of salmon in open water, the concentrations in NW-facing bays and along certain shorelines, and the behavior of individual fish we tracked.

47 Computer simulation to study the movements of adult sockeye salmon Computer salmon started off in Queen Charlotte Strait and were programmed with a range of preferred directions and also a range of levels of persistence when they encountered land. We then determined how many salmon made it to the mouth of the Fraser River, and how long it took them to get there. These values could be compared to data on real fish from tagging studies.

48 Example of a simulated salmon track

49 In general, SE orientation brought simulated fish to their goal but the most rapid travel resulted from a high degree of orientation.

50 The highest proportion of simulated fish migrated successfully when they were programmed with a moderate level of SE orientation. More stubborn fish tended to become trapped in the many inlets of the B.C. mainland.

51 Thus the twin needs, to get home and to do so in timely manner, seemed somewhat incompatible. It would seem that the fish have other means of avoiding getting trapped in the many long, narrow inlets of the coast. Perhaps they avoid fresh water that does not smell like home? More generally, however, the results indicated that some combination of homeward orientation and a set of responses to obstacles is necessary to simulate successful homeward migration in complex coastal waters.

52 What is the vertical distribution of salmon? Does it depend on oceanographic conditions? What are the movements of individual salmon? Do vertical distribution and movements reflect preferences for certain temperatures, salinities, and might they change as the fish mature and ready for upriver migration? Do vertical movements reflect efforts by salmon to detect chemical clues from their home river?

53 % of time spent at depth in two oceanographic regions Cool, vertically mixed, oceanic water Warm, stratified, estuarine water

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55 August 1985, Fish #8516 Steady homeward progress Back and forth movement in Howe Sound Resumption of steady homeward progress

56 Transitions: Ocean coast estuary - river Physical environment: 1. Temperature 2. Salinity 3. Currents 4. Land

57 Transitions: Ocean coast estuary - river Internal state of the fish: Feeding Sexual maturation Osmoregulation

58 Transitions: Ocean coast estuary - river Orientation mechanisms: Compass and map (?) Rheotaxis (flow) Odors Salinity

59 The movements of salmon in coastal waters are very complex because of the physical features of the region, and the changing internal processes in the salmon themselves. 1. Travel about km/d (varies among species) 2. Swim about 2 km/h 3. Slow down at night 4. Reactions to tides? 5. Purpose of vertical movements? 6. Variation in depth among species and areas