The Future of Food: Marine Species & Fishing Sensitivity

Future of Food: Marine Species and Their Sensitivity to Fishing

Lecture Purpose

To familiarize students with marine species harvested and consumed.
To understand how life history characteristics, diet, and trophic position influence their resilience or sensitivity to fishing.
To categorize species based on diversity and characteristics impacting their oceanic survival.

Ocean Biodiversity

The ocean is incredibly biodiverse, housing more phyla (broad taxonomic categories) than terrestrial environments, though potentially fewer species overall.
Out of approximately $34$ phyla of animals on Earth, $32$ to $34$ live in the ocean.
Examples of Phyla and Consumed Species:
- Echinoderms: Sea stars (e.g., blue starfish from Palau), sea cucumbers.
- Crustaceans: Lobster, crab.
- Tunicates (Ascidians): Consumed in Chile.
- Polychaetes (Bristle Worm): A segmented worm, related to earthworms; generally not consumed.
- Fish: Parrotfish (Caribbean), Grouper, Snapper.
- Other Invertebrates: Jellyfish (consumed in Asia).
Humans consume a vast array of marine species, including most shown on screen (except certain starfish and bristle worms).

Categorizing Marine Species for Sensitivity

Marine species can be categorized in several ways, which are crucial for assessing their sensitivity to fishing:

Taxonomic Groupings: Phyla, family, or class (e.g., parrotfish are herbivorous, eat seaweeds, and influence seafloor communities; their overfishing leads to seaweed proliferation).
Ecological Role (Diet/Trophic Position): What they eat in the food web and their trophic position is a very important trait.
Longevity and Population Growth Rate: Directly influences resilience.
Geographic Range: Broad ranges can contribute to global resilience, even with localized overfishing.
Size: An important determinant of population numbers, age at reproductive maturity, and reproductive health.

Trophic Categorization (Food Chains)

Autotrophs (Primary Producers): Organisms that obtain energy from the sun (photosynthetic organisms). They represent trophic level $1$ .
- Ocean Examples:
  - Phytoplankton: Microscopic, diverse organisms (various phyla and kingdoms); primary fuel for energy/carbon and produce about half of Earth's oxygen. They live at the ocean surface (top $50-100$ meters) due to sunlight.
  - Macroalgae: Large seaweeds (e.g., brown macroalgae from Galapagos); found in shallow, near-shore habitats with sunlight.
Heterotrophs: Organisms that eat other organisms (autotrophs or other heterotrophs).
Calculating Trophic Position: $ext{Trophic Position} = ext{1} + ext{average trophic level of its prey}$ .
- Herbivores: Eat primary producers (trophic level $1$ ), so their trophic position is $1 + 1 = 2$ . Examples: Parrotfish, sea urchins.
Caveats to Trophic Levels:
- Most organisms, even herbivores, incidentally consume some animal material (e.g., parrotfish eating tiny crustaceans/worms along with seaweed), slightly raising their calculated trophic level (e.g., $2.05$ to $2.2$ ).
- Many animals consume species from multiple trophic levels.
- Mixotrophs: Organisms that are both autotrophic and heterotrophic. Example: Corals (animals related to jellyfish) have symbiotic zooxanthellae for photosynthesis and also capture prey.
  - Anecdote: A grad student's research on coral symbiosis was funded by the Office of Naval Research with the aim of injecting symbionts into soldiers' skin for solar energy acquisition – a highly improbable concept.
High Trophic Level Example: Striped Marlin
- A top predator, eating other fish.
- Trophic position: $ext{4.5}$ (higher than most lions/tigers, which are typically $ext{4.0}$ to $ext{4.3}$ ).
- They use their bill to stun fish in schools before eating them.
Range of Trophic Positions: Generally, fish range from $2$ (pure herbivores) up to about $4.7-4.8$ . Orcas, in some contexts, can be even higher if specializing in marine mammals.

Fisheries Biology and Life History Characteristics

Fisheries biologists intensively study harvested species (range, temperature preferences, habitat, reproductive cycles, larval development).
Reproduction in Marine Animals: Often external fertilization (e.g., female fish release eggs, males release sperm, fertilization occurs in water column). Zygotes develop into larvae which drift with currents (kilometers to hundreds of kilometers), often without parental care. (Some exceptions exist, like male fish aerating eggs).
Contrasting Examples of Fish Life History and Fishing Sensitivity:
1. Sardine (e.g., in a can)
  - Past Popularity: Very popular in the U.S. in the 1930s-1950s but populations were intensely overfished and suppressed.
  - Preferred Temperature: Cold water species with a range of $7.1^ ext{o} ext{C}$ to $17.3^ ext{o} ext{C}$ .
  - Trophic Position: $ext{3.1}$ (Planktivore – eats both phytoplankton (1) and zooplankton (2)).
  - Habitat: Swims near the surface where plankton aggregates due to sunlight availability.
  - Feeding: Filters plankton through gills with mouth open.
  - Generation Time: Average of $3$ years (range $2.7$ to $3$ years).
  - Resilience to Fishing: Relatively high.
  - Minimum Population Doubling Time: $1.4$ to $4.4$ years (means a population can double in a relatively short time).
  - Implication: High growth rate allows for sustainable removal of roughly half the population annually.
2. Atlantic Bluefin Tuna
  - Distribution: Huge, warm-water range across the entire Atlantic Ocean (e.g., from Newfoundland to Puerto Rico, across to Mediterranean and Portugal).
  - Migration: Capable of crossing the Atlantic multiple times over months, documented by satellite tagging research (e.g., Margaret Watson).
  - Temperature Range: Reflects vast migratory range (e.g., winter off Connecticut $<br>ightarrow$ summer off North Carolina).
  - Trophic Level: $ext{4.5}$ (Piscivore – eats other fish like mackerel, baby tuna).
  - Physical Characteristics: Large (meter to meter and a half), incredibly fast (fusiform/torpedo-like body shape), acts like a