2009-2013 North Wales Fisheries Conference Nigel Milner APEM Ltd - - PowerPoint PPT Presentation

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2009 2013 north wales fisheries conference nigel milner
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2009-2013 North Wales Fisheries Conference Nigel Milner APEM Ltd - - PowerPoint PPT Presentation

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The Celtic Sea Trout Project 2009-2013 North Wales Fisheries Conference Nigel Milner APEM Ltd and Bangor University n.mlner@apemltd.co.uk Introduction to the CSTP BACKGROUND Historical neglect vs salmon Stock collapse focused

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SLIDE 1

Nigel Milner APEM Ltd and Bangor University

n.mlner@apemltd.co.uk

The Celtic Sea Trout Project 2009-2013

North Wales Fisheries Conference

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SLIDE 2

Introduction to the CSTP

BACKGROUND

  • Historical neglect vs salmon
  • Stock collapse – focused minds & funded R&D
  • 2004 Cardiff Symposium review ► Gaps
  • Interreg IVA funded cross-border CSTP

AIMS

  • Marine distribution, stock identity & ecology
  • Life history variation, description & causes
  • Long term collaboration + awareness

APPLICATIONS

  • Stock assessment, mixed stocks fisheries
  • Responses to pressures.. past, present and future
  • Managing risks from marine developments
  • Bio-indicator role across FW-transitional-coastal

habitats

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SLIDE 3

A basic question… why do sea trout stocks vary regionally and over time?

River A “whitling” dominated  River B average  River C high average size 0 1 2 3 Sea age (yrs)

  • Life history theory
  • Environmental variation
  • Other pressures

Changes over time

Reduction of older/larger fish  0 1 2 3 Sea age (yrs)

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SLIDE 4

Partial migration and anadromy : “To Sea or Not to Sea?”

Benefits (eggs) vs Risks (death)

Residency 4yr old “brown trout” (400eggs) 4yr old “sea trout” (6,000eggs) Smolting/Migration

Photo: Ian Davidson, DSAP

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SLIDE 5

.1+

maidens

.0+ no sea

winter “whitling”

smolts “sea trout”

.2+

maidens

Partial migration in trout

Freshwater Sea Eggs- Juveniles

Breeding adults

Performance at sea affects age structures of sea trout stocks and fisheries

Question 1: why return from sea? (Ans: spawning, complete the life cycle) Question 2: when to return? (Ans: maturation…survival, growth??? …traits related to marine habitat) Question 3: what determine proportions of sea ages? (Ans: ???LH tactics that maximise potential eggs)

Shelter?

Repeat spawners

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SLIDE 6

Sampling (2009-2012)

Marine (post-smolts and adults):

  • Beaches, estuaries, coastal, offshore
  • Trawl, seine, rods
  • 1,367 scale sets

Rivers (juveniles and adults):

  • Angler samples
  • Rod catch statistics
  • Traps
  • 5,538 adult fish scale sets
  • Electro-fishing 100 rivers, (for

genetics and microchemistry)

Scale reading, 25cm, 3.0+

Surface trawling

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SLIDE 7

Marine habitats are highly structured

Sea temperature (NB mean and range greater in east sea board) Bathymetry Seascape Currents Prey (sand eel) habitat Prey abundance

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SLIDE 8

Results

  • Trends in abundance and stock composition
  • Regional variation in life histories
  • Feeding
  • Movements and exchange
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SLIDE 9

Synchrony in catch trends, 1994-2011

  • 2.5
  • 1.5
  • 0.5

0.5 1.5 2.5

Rod catch (z-scores)

IRELAND GALLOWAY NW ENGLAND WALES Temporal variance = 34%

  • Mean catch for each country/region
  • Strong temporal coherence (Vt = 34%)
  • Common factors acting on stock?
  • Effort analysis in E&W showed very low

coherence, but high in catch and cpld

Overall smoothed, 95% CIs

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SLIDE 10

Long term changes in catches and size composition in 5 Welsh rivers, 1976-2007

  • 0.8kg = “whitling” (n.0+)
  • Increasing abundance and % of whitling
  • Reduction in N and % of larger fish in some rivers
  • Evidence of life history change
  • Time of 1st maturation, can’t exclude reduction in survival
  • 4
  • 3
  • 2
  • 1

1 2 3 4

1975 1985 1995 2005 Annual catch, z-score

<0.8kg

Teifi Dyfi Conwy Clwyd Dee

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SLIDE 11

Temporal variation in marine growth

Temp data: MAFF/Cefas

4 6 8 10 12 14 1960 1970 1980 1990 2000

Mean SST (oC)

Swansea Moelfre Heysham Port Erin PRED.TEMP

  • Sea temperature increase
  • Part of climate change

Historical data (eastern sea board)

  • Size of whitling increased 1923-2000
  • Mixed year and latitude effects
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Results

  • Trends in abundance and stock composition
  • Regional variation in life histories
  • Feeding
  • Movements and exchange
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SLIDE 13

10 20 30 40 50 60 70 80 90

TYWI LUNE Dyfi TAWE RIBB NITH TEIFI B.ESK CURR IoM LUCE CONW BAND ARGI DEEw FLEE CLWY BOYN EHEN SHIM DEWR CAST SLAN

% occurrence

1 2 3 4 5 6

Variation in sea ages of sea trout

(from scale reading)

6yrs

Multi-age Dominated by whitling

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SLIDE 14

Spatial variation in marine growth, mean length(mm) at age n.0+

Between-river variation in length of n.0+ sea trout in 23 Irish Sea rivers

| Seaboard:a LAT < 53.309 370.2 304.6 284.0

Tawe(393) Tywi(373) Teif(375) Dyfi(388) Deew(347) Conwy(345) Clywd(315) Ribble(285) Lune(332) IoM(400) Ehen(311) Fleet(273) Luce(304) Nith(310) B.Esk(313) Shimna(235) Bandon(273) Slaney(276) DeeWR(279) Castletown(280) Argideen(286) Boyne(322) Currane(321)

  • Smaller on western sea board
  • Latitude effect on east coast (larger in

more southerly rivers)

  • Caution, smolt length and age

Sea board: E-W LAT<53.3

50 100 150 200 250 300 350 400 450

Mean length (mm)

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SLIDE 15

Spatial variation in survival (%)

Length<296mm Temp <11.15oC

  • Lower % S in popn of smaller size fish
  • Lower % S in cooler waters (Irish

coast & more northerly sites of eastern sea board)

10 20 30 40 50 60 70 80

IOMA FLEE LUCE NITH BESK BAND SLAN DEWR BOYN ARGI CAST CURR SHIM RIBB EHEN LUNE TAWE CONW CLWY TEIFI DEEw DYFI TYWI

Annual survival (%)

y(B.Esk) = -1.4238x + 7.03 R² = 0.998 y(Tywi) = -0.781x + 5.86 R² = 0.890

1 2 3 4 5 6 7

1 2 3 4 5 6 7 8 9 10

ln(N+1) Sea age (t) yrs

%S, after marine yr 1, from sea age structure (=e(z+ln100))

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SLIDE 16

Regional summary of growth and survival (selected by tree regression)

Low growth Medium survival High growth High survival Low growth Low survival High growth Medium survival

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SLIDE 17

Life history responses to 1st year marine growth

  • Marine survival (post 0+)

increases with 2.0+ length (N=23

R2=0.404,p<0.01)

  • Is earlier maturation a response to maximise reproductive opportunity in the face of marine

environmental influence on growth and survival?

Currane

10 20 30 40 50 60 70 80

200 250 300 350 400

Survival yr 1% Mean length, n.0+ (mm)

East West

  • Time of first return (as % 2.0+)

decreases with 2.0+ length (N=23

R2=0.288,p<0.01)

Currane

10 20 30 40 50 60 70 80 90

200 250 300 350 400

% n.o+ in population Mean length, n.0+ (mm)

East West

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SLIDE 18

Results

  • Trends in abundance and stock composition
  • Regional variation in life histories
  • Feeding
  • Movements and exchange
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SLIDE 19

Adult sea trout prefer to eat fish

Regional variation Prey (sprat) abundance

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SLIDE 20

Results

  • Trends in abundance and stock composition
  • Regional variation in life histories
  • Feeding
  • Movements and exchange
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SLIDE 21

Hydrodynamic Modelling (Cefas)

General Estuarine Transport Model (GETM), simulates particle (=“fish”) movements, run from April 1st Slaney Shimna Dyfi Tywi

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SLIDE 22

Genetic and microchemistry/radio isotope assignment of marine-caught fish to regions

9 putative genetic regions identified by juvenile samples, 99 rivers Marine samples assigned to regions by Oncor/GeneClass consensus

  • Microchem origins based on 36 rivers
  • δ15N suggested mainly coastal residency

& some exchange

Solway/Morecombe SE Ireland

Overall: most fish remain “local”; evidence of some extensive exchange, can’t quantify due to small sample sizes

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Conclusions

  • LIFE HISTORIES and MARINE ECOLOGY
  • Evidence of synchronous variation indicates response to common marine factor/s (can’t yet

rule out FW factors too)

  • Stock structure variation reflects shifts in time of 1st return, likely due to growth and survival
  • Regional growth variation linked to temperature (+ food?)..….HABITAT
  • Long term temporal growth variation cause remains uncertain (probably climate)
  • Consistent with limited dispersal, reflecting marine hydro-graphic and environmental factors.
  • BUT some extensive dispersal demonstrated by genetics, microchemistry and modelling
  • 4
  • 3
  • 2
  • 1
1 2 3 4

1975 1985 1995 2005 Annual catch, z-score

<0.8kg

Teifi Dyfi Conwy Clwyd Dee
  • MANAGEMENT & MONITORING
  • Broad-scale conservation: does partial synchrony imply meta-population effects, conferring

resilience and stability on individual rivers? (role of small streams?)

  • Cross-border management of marine phase is indicated by the synchrony and partial dispersal
  • Catch recording is weak and a major limitation: size data, fishing effort
  • Marine food chain is important for sea trout, but key indicators are poorly monitored
  • Marine habitat monitoring and protection are important for sea trout
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SLIDE 24

Thanks to all the sponsors and many co-workers

… and many ‘00s of anglers