Fisheries Science Lecture Notes

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MSCI 458 - R. Young, Coastal Carolina University

***Final Exam: The notes for the new material for the exam start HERE

Introduction

What is a fishery?

Miller and Johnson's (1981) definition is "a union of aquatic organisms and humans"
I like my own: "a consumptive harvest of wild aquatic resources"

Consumed for food and for industry (fish meal, animal feed, fertilizer, oil…)
Not just fish -- various shellfish and crustaceans, squid, marine mammals, turtles…

Though related, a fishery is not aquaculture (although hatchery-based fisheries blur the line)

3 basic elements of a fishery:

the resource itself
the aquatic environment
people (fishermen, seafood companies, even the broader scope of everyone who influences the habitat)

Conservation and management

fisheries conservation is the "wise, sustainable use of wild (naturally produced) fisheries resources."
Much of fisheries management is simply conservation, but active management occurs in fisheries such as those supplemented by hatcheries (i.e. managed and enhanced, not just conserved wisely)

Ancient History

2300 BC - government fishing fleets in Sumaria near Persian Gulf (nets, hook and line)
2000 BC - aquaculture in China for carp and other freshwater fish (473 BC, Fan Lee wrote a book on carp aquaculture)
1400 BC - Egyptian elite were fishing for recreation (vs. food)
fishermen prominent in Old and New Testament
Fishery regulations in ancient Rome, feudal England, Mass Bay Colony
Fisheries drove exploration of new world (cod and whaling)

Recent History (from your book and from Greenpeace web page, "Amazing facts about the global fisheries crisis")

Worldwide fisheries harvest seems to have reached a plateau in the last 2 decades at around 85-90 million metric tons (mmt)

Increased over 4 times since 1950 (from 18.5 million tons in 1950) (Greenpeace)
Another 25 mmt or more each year is thrown back as bycatch--most won't survive (Greenpeace)

Since 1970, the world's fishing fleet expanded twice as fast as the world catch (Greenpeace)

overcapacity means pressure to exploit
as a whole, the world fishing fleet has been operating at a multi-billion dollar deficit each year through much of the 1990's (Greenpeace)

Worldwide, about 13 million people make all or a major part of their living from fishing (Greenpeace)

Combined with their immediate families, about 50 million people are directly dependent of fishing (Greenpeace)
Another 150 million people are employed on land, processing fish and servicing fleets as part of their jobs (Greenpeace)
In the U.S., about 300,000 people are employed in coastal-related fisheries alone

The average U.S. citizen eats 16 pounds of fish/shellfish per year

For two thirds of the world's population, fish make up about 40% of their protein consumed (Greenpeace)
Although the amount of fish consumed be people each year has increased with the world catch, the proportion of the catch going to people has decreased (roughly 25-30% goes to fish meal for livestock, etc…) (Greenpeace)

Recreational fishing is not to be overlooked:

In 1990, 36 million people age 16 and over went fishing
The money they spent supported the equivalent of 600,000 full-time jobs in fishing related industries

Fishery trends at the international, national, and regional level

We spent a lot of time reviewing some basic fishery trends at various levels and for various species. Consult your presentation handout and notes.

Aquatic Productivity and Fisheries

The main point: Primary production in the oceans supports many trophic pathways, only some of which are productive for fisheries. Fisheries production (growth and reproduction) at exploitable levels is restricted by physical and biological factors to specific areas.
We tend to view different taxonomic levels with a taxonomic bias.

For example we might think of "phytoplankton" as primary producers and yellowfin tuna as a top predator. "Phytoplankton" is a gross generalization, that includes thousands of species with various and sundry characteristics. We do not generalize flounders, tuna, and anchovies as simply "fish" with the same behavior and ecological role, so why would we lump a diatom and cyanobacteria together into one homogenous category?

Long food chains and significant microbial loops will limit total fisheries production at higher trophic levels.
Trophic transfer efficiency (TE) is believe to average around 10%, but can vary under certain conditions and for different groups.

Up to 20% for some bacterial transfers

Changes in gross growth efficiency (GGE) can alter TE

As the costs of obtaining food go down, the proportion of energy allocated toward growth increases
Locomotion costs represent 2-3 X the standard metabolic rate (SMR) for a typical fish at optimal speed (minimum cost of transport)

So, GGE and therefore TE go up if prey densities are high and locomotion and capture costs are low

Fished species

Important invertebrate fisheries:

Molluscs (clams, oysters, mussels, scallops, cepalopods)
Crustaceans (shrimp, crabs, lobster)
Echinoderms (urchins, sea cucumbers)

A partial list of important vertebrate fisheries:

Engraulidae (anchovy) and Clupeids (Atlantic herring, sardines, menhaden, alewives, shad, sprat) – 27% global catch in 1990
Gadidae – cod, Pollack
hakes
dolphinfish (mahi mahi)
triggerfish
Sciaenidae – drums
Salmonidae – salmon, trout, char
Serranidae – groupers, seabass
Scorpaenidae – rockfish, scorpion fish
Carangidae – jacks
Lutjanidae - snappers
Mugilidae – mullet
Scombridae—tunas and mackerels
Bothidae/Pleronectidae – flounders, halibut
Elasmobranchs – sharks and rays

Abundance

(I think lab 1 covered it pretty well – the obvious point is that we would like to know it exactly, but our estimates usually have a large confidence interval)

Growth

Fish grow their whole lives and rates are highly variable

Indeterminate growth (most fished species)

Variable size increases
Sexually mature before reach max size

Determinate growth

Ex/ crustaceans that undergo molts to grow
Predictable size increases
Sexually mature at max size

Increased size = less predation risk, greater energy storage and size to withstand resource fluctuations, increased fecundity and ability to compete for mates
Changes with life stage

Grow most rapidly early in life (exponential curve, initially)
Growth slows at sexual maturity (energy into gametes, which are lost eventually, unlike body mass: gonadal vs. somatic growth)

Exponential growth curve "breaks" to form a sigmoid curve

Growth curve nearly plateaus when older (larger maintenance cost, more into reproduction)

Variation within species

Fast and slow growing fishes

Fast- may reach sexual maturity earlier, but ultimate size is less (often shooting for critical size by a specific season)
Slow-reach sexual maturity later, but grow more (longer time without emphasizing gonadal growth)

Male/female differences

Often, females mature later ("deferred maturity")

larger size=more eggs

Males of some species have deferred maturity

Typically when males have nests or territories and larger size =more mating events (somewhat mammalian)

Environmental factors on growth

Temperatue and salinity have direct effects on metabolism
Temperature, salinity, rainfall/run-off, etc. effect primary production
Changes in water levels for freshwater fishes
Random encounters of patches -- some fish get big advantage early on simply by chance

Density-dependence

Refers to intra-specific competition
A wide variety of results and opinions

Abundance will affect growth ONLY IF resources are limiting
Limitation fluctuates with fish population size and with carrying capacity (neither stay constant)
Often exploited populations are held at a reduced population size
Density-dependent growth most obvious in years of very high abundance or years of depleted carrying capacity

Modeling growth

Von Bertalanffy growth equation (1938)

Most commonly used, but many exist
Originally developed as a model for human growth processes, and based in part on the balance between anabolism and catabolism
Exponential curve, rather than sigmoid. Thus:

works best for length rather than weight
works best for older segments of the population (when larval stages and early juveniles are a prominent component of the age range, a sigmoid curve is likely).

Formula:

L_t = L_inf (1-e^-k(t-t0)), where

L_t = length at time (actually age) t
L_inf = maximum (asymptotic) length
K = Brody growth coefficient, or the rate at which L_inf is achieved (not a growth rate, but a measure of the rate at which the growth rate declines)
T₀ = theoretical age at which the fish would have zero length, according to the model

Generally, a high K is associated with fast early growth, low age and size t maturity, high reproductive output, short life span, and short max length

Fishing gears and techniques

This is not a complete survey of all the gear and techniques covered in your text, although it has some additional information. You are responsible for all the information in your text.

Harvesting Methods (consult pictures in your text)

Hook and Line Gear

Hooks - single, trebble, circle, barbed vs. barbless
Bait - live bait, cut bait, lures, chumming
Longlines

Also trotlines or setlines
Baited hooks and gangions on mainlines
Usually set on bottom or near surface
Spacing of gangions and materials for lines (ropes, monofilament, wire…) effects capture
Tunas, sharks, billfish, halibut, others…

Active hook and line

Pole-fishing, hand lines, power reels
Drop fishing vs. trolling (not trawling!!)

Active Entrapment Gear

Trawls

Bottom, midwater, and surface trawls
Lead or chain line on bottom (sometimes with rollers or bobbins), float or cork line on top
Some sort of spreader (otter doors vs. beam trawl)
Codend
Effective capture, but often with high bycatch (can partially control with mesh size) and benthic habitat destruction

Dredges

Rigid framed gear
Dig in or drag and disturb the bottom, usually to dislodge or scoop up bivalves (oyster and scallop dredge)

Seines

Long rectangular nets (much longer than deep), again with leadline and floatline
Beach or haul seines

For shallow water, set and hauled by boat or by hand

Purse seines

Large deepwater nets
Set in a circle, then pull purse line to form a bowl, then haul in catch
Good for oceanic schooling fishes (menhaden, tuna…)

Passive Entrapment Gear

Trap nets

Long barriers of netting (leads or wings) extend typically from the shoreline angling toward an entrapment net
Entrapment area is typically a series of connected funnels (some sort of fyke or hoop net)
Use to capture fish that move along the shoreline

Pound nets

A slightly more permanent trap net
Wings and sometimes entrapment area set with semi-permenent stakes

Weirs

Even more permanent version of trap net.
Wings are woven walls of brush, or sometimes actual solid walls of rocks or concrete

Trap nets, pound nets, and weirs are very effective against coastal migratory species -- restricted in many areas
Pots and traps
Usually pots catch invertebrates (lobster, crab) and traps catch fish
Soak time of nets and traps effects performance

Entanglement Gear

Gill nets

Size selective - smaller fish pass through mesh, larger fish can't get head in to be gilled

Trammel nets

Entangle fish, but don't gill them
2 small mesh panels on either side of central large mesh panel
fish pushes smaller mesh through large mesh, catching itself in a pouch
not very size selective, but useful for catch and release with minimal damage

How do you find the fish? - advances in technology

Fish finder sonar
Hydrophones
Spotter planes and helicopters
Satellite images of thermal fronts and plankton blooms

Various Life History and Basic Fish Biology Topics:

Age at Sexual Maturity

Does size matter? -- yes, probably more than age

Age of maturity varies with growth rate (as described above), but often the critical size is the same regardless
Especially for larger, longer-lived species (many smaller fish mature after 1 or 2 years, anyway)
In some cases, size of maturity can decrease as well

Compensatory reaction to fishing:

Growth rate increases and age of maturity decreases (how does this happen?)
ex. Herring growth rate increased 25% and age of maturity decreased by 2 years with a growing fishery (Murphy, 1977)

Age of maturity and mortality

Evolutionary pressures
If likely to die early, better mature early and hope to reproduce at least once

Ex. Scup: 80% juvenile mortality rate, reproduce at age 2

If juvenile mortality risk isn't so bad, but reproductive risk is big, better grow large first to get the most out of that reproductive event

Ex. Atlantic sturgeon (mature at 28 years old), spiny dogfish (mature at 12 years old or more), salmon--be anadromous to grow large

Age of maturity versus lifetime offspring production

Early maturity at a smaller size may offset late maturity at a large size by providing more lifetime spawning seasons
This balance tips the other way the longer larger fish live (high fecundity for large fish)
Mix of successful strategies varies by species and by situation

Ex. - slow-growing Atlantic salmon may mature after 1 year at sea, but fast-growing salmon mature after 2-3 years
Seems backwards, but predation risk for slow-growers in the ocean is high--so reproduce early

Sex reversals and sex ratios

· Dioecious - distinct male and female sexes

· Hermaphroditic - sequential or simultaneous

o Protandrous - male, then female

o Protogynous - female, then male

· Why be a simultaneous hermaphrodite?

o Differential advantage according to sex for various sizes

o Examples

§ if size enhances competition for mates/territoriality, large males can maximize reproductive output

§ if above is untrue, large females can maximize fecundity and therefore reproductive output

§ protogynous is more common, especially among fished species (especially groupers and sea basses (Serranidae), and parrotfishes and wrasses)

· sex ratios skewed in sequential hermaphroditic species, and targeting fisheries can potentially skew them further to point of collapse

o example: Protogynous groupers

§ Hermaphrodites - start as females, large adults become males (opposite of and more common than protandrous hermaphrodites)

§ Sex ratio skewed toward significantly more females

§ Large and spatio-termporally predictable spawning aggregations susceptible to heavy fishing pressure

§ Fisheries target large fish (more males removed

§ If males removed early enough, largest females will change sex

1. Leaves fewer females for that year

2. Leaves smaller females that year (less fecund)

§ If males removed too late, largest females will start to change sex, but won't complete process in time

1. Same problem as above, plus fewer males as well (double whammy)

Reproductive Schedule

How often and how many times do you spawn?
Iteroparity versus semelparity

Strategies for maximum lifetime fecundity

Depends on number of offspring per spawning event and likelihood of survival for future spawnings
Survival and future spawning requires:

Survival from predation during spawning
Recovery from physiological stress of reproduction
Weakened, vulnerable to infection, disease, predation
New gonadal growth
Stress can be high enough to go years in between spawning

Shortnose sturgeon may go 8 years
Atlantic salmon with long freshwater migrations may skip a year, but those with short river migrations spawn every year

If you don't have to worry about this, can put more into one reproductive event

American shad example:

All anadramous, coastal migrators as adults
Southern spawners are semelparous, northern spawners are iteroparous usually

Florida fish mature at younger age and smaller size than New Brunswick fish
Florida fish produce 3 times as many eggs as do first time spawners in New Brunswick (and on average, twice as many eggs in a lifetime)
Florida fish use 70-80% of energy reserves to spawn versus 40-60% for New Brunswick fish
Semelparous fish have a greater average number of offspring per female than iteroparous New Brunswick fish (lifetime totals)

Then why be iteroparous at all?

Greater variability in spawning rivers in north (temperature especially) means some years might have poor survival -- better to spread risk across years

Batch spawners

Typically iteroparous
Release eggs in batches over periods of days, weeks, or months
Ex/ Norwegian cod - 50-250,000 eggs per batch at 3-day intervals over a spawning season of 50 days

Fecundity

Number of eggs produced by a female (per spawning season)
Why not a male? - no correlation between number of sperm and number of offspring
Variability in fecundity
Oviparous, ovoviviparous, and viviparous -- generally much higher fecundity in oviparous species
Fecundity varies with body size and species

Atlantic cod: 200,000 (small females) to 12 million eggs (large females)
Smallmouth bass: 2,000 eggs (small females) to 20,000 eggs (large females)
Ocean sunfish up to 300 million eggs per year

Fecundity increases exponentially with size

F = aL^b, where F is fecundity, L is length, and a and b are species-specific coefficients
Increase in F relative to length is greater (even more exponential) than increase in W (weight) relative to length, so relative fecundity (fecundity per unit mass) increases with size.

Why the big increase with size? - are large adult female cod really 60 times larger than small adult females? No

Apportion energy differently depending on life stage (growth vs. metabolism vs. reproduction)
The longer you live, the less important further survival becomes--take risks for more reproductive success
Example: shad - southern shad (semelparous) is much more fecund than northern shad (iteroparous)

Fecundity vs. egg size vs. larval size

Egg and larval size typically inverse relationship with fecundity

Typical oceanic pattern is many small eggs
Good strategy to exploit patchy food resources

Survival rate and fecundity also typically inverse relationship
Extremes on low fecundity and high survival/egg size/larval size are sharks and many species with benthic eggs

Parental Care

What is parental care?

Includes any combination of post-spawning care of eggs and/or larvae
Includes other reproductive specializations which increase survival, including internal fertilization, direct nourishment of eggs, etc…

Parental care and fecundity generally inversely related
Types:

Broadcast spawning (minimal care)

Ocean spawners - usually pelagic eggs
Freshwater/estuarine spawners - usually demersal eggs

Egg scatterers

Lay demersal eggs on specific substrates, but don't modify them (build nests)
Exs. - sand lance on cont. shelf sand and winter flounder on estuarine sand, walleye over gravel/boulder, Atlantic silversides on intertidal filamentous algae mats (keep moist and hidden)

Shelter spawners

Many species lay demersal eggs in crevices, nooks, etc
Some lay eggs on live inverts (sea ravens and sculpins on sponges, etc.)

Nest builders

Many in gravel (good aeration and protection) - lamprey, salmon and trout (redds), fallfish (see picture in book)
Depressions in sediment - sunfishes, freshwater bass
On vegetative material - damselfish and garibaldi (algal matt), sticklebacks construct tubular nests of fragments of vegetation

Guarding

Many nest builders then guard (damselfish)
Why benefit males more? (attract more mates?) - your book takes this view only
Or is it females that benefit? (less energy for parental care--more for egg production?)
There are also alternative "cheating" strategies for subordinate males

Brooding

Internal (ovoviviparous and viviparous elasmobranchs, guppies, etc.- carry eggs inside until hatch/born)
External - carry fertilized eggs or larvae outside of female's reproductive tract (pouches, mouths, gills, etc..)

Recruitment

Recruitment is the addition of new individuals through reproduction and growth

Used differently depending on context

Recruitment to spawning population
Recruitment to the fishery (the harvestable population)
Recruitment to a reef or substrate
Larval recruitment of demersal species (i.e. "settlement")
Recruitment to "metamorphosis" stage

Recruitment varies greatly from year to year

Routinely varies by a factor of 20 in many species
Abundance of any given year-class or cohort within the fish population is not predictable
Common to have population dominated by one or a few year-classes

Fisheries have often failed to match removal rates with recruitment, often for complex reasons

Lake sturgeon in Great Lakes