Housekeeping. WF4133 Fisheries Science. Quick review. In the news. Direct enumeration 2/7/2018 HOW DO WE MEASURE & QUANTIFY RECRUITMENT?

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1 WF4133 Fisheries Science Module 2: Fish and fish population dynamics Class 7 Housekeeping Lab today... Now is the time to be looking for summer jobs! State websites USA jobs Fisheries.org Texas A&M Quick review In the news 1. ecruitment 2. ecruitment variability 3. Quantifying recruitment html Direct enumeration 1. Active: get out there and count! 2. Passive: set some gear and come back Can also exploit life history HOW DO WE MEASUE & QUANTIFY ECUITMENT? CONT 1

2 Active: Observe and count Yep snorkeling for fish! Active: Capture and count Actively capture fish Trawling Get to the choppa so we can count redds! Electrofishing Cast netting Passive: Capture and count Set traps Smolt trap Minnow trap Indirect approaches We model the population to infer recruitment Virtual population analysis Population models Light trap Fyke trap 2

3 Linking recruits and fish We need to relate the number of fish, or spawners, to recruitment to forecast and understand fish population dynamics HOW DO WE LINK ECUITMENT AND FISH ecruits Fish r versus K selection Stable environments tend to make few, "expensive" offspring Nest guarders, mouth brooders lots of parental care Unstable environments tend to make many, "cheap" offspring. Broadcast spawners no parental care Parental care Spectrum of parental care forms None: Broadcast spawning 1. None 2. Hiding 3. Guarders 4. Brooders & live bearers. Feeders Common carp spawning aggregation Lake sturgeon spawning aggregation 3

4 Egg hiding The simplest form of fish parental care Egg Guarding Tend and defend eggs, embryos, or larvae until they hatch Bull trout redd Lamprey redd May build nests or choose an area (cavity, cave or natural burrow, underside of a rock, or log) as a spawning and guarding site Brooders and live bearers Protect their young internally and some even have live births known as live bearing or viviparous species Feeding Most complex or elaborate parental care behaviors found in fishes are undoubtedly the Feeding young post hatch and caring for nutritionally independent young Discus (Symphysodon spp.) young as well as the young of some other cichlid species ingest the epidermalmucus from their parents body. Extremely rare in fisheries ecruitment Year ecruitment Immigration Mortality Emmigration Initial population = 4

5 What s wrong with these dynamics? Linking recruits and fish 1 Abundance ecruits Fish Years This is key! Stock recruit relationship ecruits/spawner relationship ecruits What do you expect this relationship to look like? ecruits per spawner What do you expect this relationship to look like? Some principles for stock recruit models 1. Must pass through origin 2. ecruits must exceed spawners over some part of the ranges of stock size Stock recruit relationship ecruits a b ecruits Is this biologically reasonable?

6 ecruits per spawner ecruits/spawner relationship ecruits Spawner a ecruitment does not change with increasing stock abundance Density independent if Number of recruits increases at a constant rate (i.e., b) ecruits per spawner is constant (i.e., a)for all numbers of spawners. ecruits ecruits per spawner ecruits a b Spawner ecruits Spawner a ecruitment does not change with increasing stock abundance Is this biologically reasonable? Stock recruit relationship ecruits/spawner relationship ecruits ecruitment changes non linearly with stock abundance Is this biologically reasonable? ecruits per spawner ecruitment per spawner changes with increasing stock abundance Is this biologically reasonable? Why? Density Dependence if Putting them all together Number of recruits does not increase at a constant rate ecruits per spawner decreases with increasing number of spawners ecruits ecruits per spawner ecruitment changes non linearly with stock abundance ecruitment per spawner changes with increasing stock abundance ecruits Density dependent 6

7 Stock recruit relationships 1. Beverton Holt 2. icker 3. Sheperd 4. Others exist but these are the biggies ecruitment model important moments Maximum recruits what is the number of recruits? Maximum recruits/spawner where is the number of recruits per spawner the highest? Beverton Holt (197) Beverton Holt: Maximum ecruit ecruits (x1) a 1bSpawers a 2 b.4 ecruits (x1) a b ecruits/ Maximum recruits/spawner S S a ecruits (x1) Beverton Holt Maximum /S a bspawers a 2 b.4 Maximum 7

8 Beverton Holt Asymptotic recruitment ecruits limited by: Food Space Habitat Many marine species ecruits (x1) icker (194) ase a 2 b.4 bs. icker: Maximum recruits icker: ecruits/spawner ecruits (x1) a b e 2.4 e 24.9 ecruits/ S S a 2. icker icker model ecruits (x1) Maximum /S Maximum ase a 2 b.4 bs ecruitment declines at high stock sizes ecruits limited by cannibalism, redd superimposition Typical for anadromous species. 8

9 Beverton Holt and icker Shepherd model (1982) Both models contain density dependent and density independent terms Compensatory mortality reduces recruitment at high stock levels ecruits (x1) a 1b Spawers a 2 b.4 c. Shepherd : Maximum recruits Shepherd : Maximum /S ecruits (x1) a ( 1)/ ( b ( c c c 1) bc 2 (.4 (1. 1) (1.1)/1. ecruits/ Shepherd model is flexible Sheperd model ecruits (x1) 1 1 C=.8 C=1 c<1 density independent c=1 Beverton Holt model c>1 icker model C=1.1 9

10 Which model would you fit? Hilborn and Walters (1992) conclude: Analysis of stockrecruitment data provides an enormous number of traps for the unwary good luck ecruits (x1) By pm February 9th See link on course website. points