Multi-jurisdictional fisheries and toxic algal blooms...

[RLLigman]

Fish populations exploited by Man have been traditionally managed via fishing zones or seasons established within the confines and constraints of jurisdictional boundaries. Unfortunately, for some odd reason, fish pay scant attention to maps... Sub-populations within a given species that have seperate and distinct spawning sites and consequent genetics are classified as demes;they may individually possess altered growth and reproductive capacities, as well as numeric abundance, but mix and move as an amalgam of the total fish stock during the interval where they are exposed to exploitation via a commercial or sport fishery. Obviously, this increases the risk of overexploitation of those demes that are under represented in the total stock, since their removal rate as a fishery catch component may be disproportionately high relative to total stock numbers. Sadly, since many of the fishery catch statistics(stock recruitment models, catch at age stock composition models, etc.) assessment models employ data gathered within these arbitrarilly designated assessment zones, which in many cases have somewhere between limited and zero relavance to what is actually happening to the fish stock within a vast water body like Chesapeake Bay...or an individual Great Lake. Sadly, many fish and game management agencies are very "hidebound" preferring to cling to a invalid paradigm. You have to scratch your head when you consider that Man is one of the most highly adaptive critters on this planet, yet he is also one of the most resistant to change...

 

[RLLigman]

Steve Sutton, those floating scum algae pods are likely blue-greens, which possess an organelle called a heterocyst that enables them to "tap" atmospheric nitrogen to augment growth, thus, they are able to outcompete green algae and diatoms when dissolved nitrogen becoms a growth limiting factor within a phytoplankton population. There are three sources of nitrogen and phosphorus available to freshwater and brackish water algal populations: point source discharge, overland runoff, and atmospheric dry fallout. Two background pathways are likely to be contributing to the phytoplankton population shifts within the Indian River systemvergrazing of zooplankton populations by fish species within the system, and/or, cold temperature driven dieoffs within the zooplankton population array. If Cladoceran zooplankton population numbers remain at high density they are capable of holding the phytoplankton population in check via their collective grazing rate, maintaining a roughly static species composition and proportional density array within the algae population. Should fish stocks of filter feeding fish deplete these large body herbivorous zooplankton, green algae and diatom populations expand to the point where their density begins to deplete dissolved nitrogen concentrations, enabling blue-green algae to gain a competitive advantage via their inherent ability to "tap"atmospheric nitrogen stores to continue to grow and expand their number and density. While filter feeding fish do ingest blue-green algae, many traverse the entire digestive tract and are "pooped out" intact and still capable of photosynthetic activity. The same coating that enables them to float also enables them to remain nearly completely resistant to digestive enzyme degredation within an individual fish's gut.

Since there were both brown algae as well as blue-green blooms within the Indian River lagoon system over the last two years, I would put my money on cold temperature induced die-offs within the zooplankton population as the principal background influence on algal community array shifts. The big downside is that the brown algae blooms you have experienced depress zooplankton stock recovery rates...prolonging the adverse water quality impact intervals. Federal clean water/clean air standards enacted nearly thirty years ago via NEPA passage have had broad beneficial impacts on atmospheric dry fallout and point source nitrogen and phosphorus inflow rates within aquatic ecosystems, so I would look at specific point source N/P inflows, as well as overland runoff rates and sources from agricultural sites and waterfront palatial lawns as the principal sources.

 

[Jeff Reardon]

Steve Sutton, those floating scum algae pods are likely blue-greens, which possess an organelle called a heterocyst that enables them to "tap" atmospheric nitrogen to augment growth, thus, they are able to outcompete green algae and diatoms when dissolved nitrogen becoms a growth limiting factor within a phytoplankton population. There are three sources of nitrogen and phosphorus available to freshwater and brackish water algal populations: point source discharge, overland runoff, and atmospheric dry fallout. Two background pathways are likely to be contributing to the phytoplankton population shifts within the Indian River systemvergrazing of zooplankton populations by fish species within the system, and/or, cold temperature driven dieoffs within the zooplankton population array. If Cladoceran zooplankton population numbers remain at high density they are capable of holding the phytoplankton population in check via their collective grazing rate, maintaining a roughly static species composition and proportional density array within the algae population. Should fish stocks of filter feeding fish deplete these large body herbivorous zooplankton, green algae and diatom populations expand to the point where their density begins to deplete dissolved nitrogen concentrations, enabling blue-green algae to gain a competitive advantage via their inherent ability to "tap"atmospheric nitrogen stores to continue to grow and expand their number and density. While filter feeding fish do ingest blue-green algae, many traverse the entire digestive tract and are "pooped out" intact and still capable of photosynthetic activity. The same coating that enables them to float also enables them to remain nearly completely resistant to digestive enzyme degredation within an individual fish's gut.

Since there were both brown algae as well as blue-green blooms within the Indian River lagoon system over the last two years, I would put my money on cold temperature induced die-offs within the zooplankton population as the principal background influence on algal community array shifts. The big downside is that the brown algae blooms you have experienced depress zooplankton stock recovery rates...prolonging the adverse water quality impact intervals. Federal clean water/clean air standards enacted nearly thirty years ago via NEPA passage have had broad beneficial impacts on atmospheric dry fallout and point source nitrogen and phosphorus inflow rates within aquatic ecosystems, so I would look at specific point source N/P inflows, as well as overland runoff rates and sources from agricultural sites and waterfront palatial lawns as the principal sources.

Mr. Ligman--don't disagree with a single thing you say. I don't know much about Indian River algal blooms, but we face similar issues on (over) developed lakes in my part of Maine every summer. But isn't it putting the cart before the horse (or some such metaphor) to start by blaming the planktivorous fish, or perhaps the weather, and only at the end consider addressing the fundamental problem, which is nutrient enrichment driven by various human activities?

My favorite example of this kind of thinking was a local effort to "fix" the plankton problem on a local lake by removing "voracious planktivorous fish" who were thought to be affecting the local population of zooplankton that would otherwise have helped keep algae blooms in check. The experiment ended with at best mixed results after a great deal of money was spent and piles of removed white perch were removed to be composted. It always seemed to me the money could have been better invested in planting buffers in front of fertilized lawns or upgrading a campowners few failed septic systems.

 

[RLLigman]

Actually, you are spot-on correct in the root cause and fix;humans poop and pee phosphorus and nitrogen, as well as over applying it via fertilizer to their lawns, golf courses, and agricultural lands. That said, this issue has been in place in human populated Florida lakes and waterways for a long time with little or no progress being made by EPA or Florida Fish and Game. My comments were directed at the specifics of why these blooms have increased in frequency, duration, and intensity in recent years.

There are some other issues tied to the similar Microsistis sp. blooms that shut-down the water intake for Toledo in Lake Erie last year. EPA officials feel that, if they can reign-in agricultural fertilizer over-applications and poorly time applications, they can decrease runoff rates enough to significantly address the problem.