Material and Energy Flow in Aquaculture Question for the Day Does aquaculture supply us with more food than would be available without aquaculture? We’ll spend this section discussing that question and working through two specific examples. Fifty-five percent of all major global are considered fully exploited or overexploited. (Goldburg and Triplett 1997, Naylor et al. 1998) The capture fisheries are around 85-95 million metric tons per year (Mt = million metric tons = billion kg, trillion g) (Naylor et al. 2000) and have plateaued at that level. There has been a gradual shift in the fishing industry from large high-value, carnivorous species, to smaller, lower value, higher growth rate species that feed at lower trophic levels. (Pauly et al. 1998. Fishing down marine webs. Science 279 860- 863. As a consequence, global aquaculture production is rising. In 1988, the total was 10 Mt. In 1997 the total was 29 Mt. In 1997, aquaculture supplied 18.5% of the global seafood supply and 27% of the seafood eaten by humans. One might imagine that aquaculture would have a number of advantages over capture fisheries. It might lessen pressure on overexploited capture fisheries. Fish and shellfish have high feed conversion efficiencies so they are more efficient sources of protein than cattle. Their high feed conversion efficiencies are due in part to the fact that they are cold blooded so they don’t expend energy keeping themselves warm and they are supported by water so they don’t expend energy holding themselves up. Cattle convert feed to biomass with an efficiency of about 8:1, Pigs, 6:1, poultry, 3:1 Certain Salmon breeds convert at an efficiency of about 1.1:1 or 1.2:1 (Weber, Michael L. 2002, Farming Salmon, a briefing Book. HTTP//www.seaweb.org/resources/sac/contents.html) People generally eat a higher proportion of fish than of terrestrial vertebrates – i.e. they can eat more of the fish than they do a cow. For example, people generally eat 50%-60% of raw weight of finfish, while only 40% of the raw weight of a sheep. (probably from goldburg but should be checked). The aquaculture industry is pretty diverse. The global production (by weight) includes 46% freshwater fish, 25% aquatic plants,18% mollusks, 7% diadromous and marine fish, and 4% crustaceans. China is the largest producer of aquaculture, producing 57% of the global total. The most abundant aquaculture species are freshwater species. This is particularly true in Asia. The asian carp based systems dominate the global production. Over 5,000 Kt are produced annually, which is nearly 1/3 of the global aquaculture total. Polyculture is possible, with little artificial inputs. The common carp is a benthic detritivore, the grass carp is a macrophyte feeder, the silver carp is a phytoplankton filter feeder and the bighead carp is a zooplankton feeder. Atlantic salmon, which is the aquaculture species that captures most US attention, is about 2% of global total Channel Catfish is about 1% of global total United States US Aquaculture Production. Major Species Species Quantity MT Percent US Total Catfish 202,706 49.0% Oysters (w/shell) 109,080 26.4% Crawfish 26,375 6.4% Trout 25,240 6.1% Salmon 14,106 3.4% Clams 13,481 3.3% Baitfish 9,883 2.4% Tilapia 6,838 1.7% Hybrid Striped Bass 3,772 0.9% Marine Shrimp 1,000 0.2% Mussels 930 0.2% Sturgeon 20 0.0% Total 413,431 (from Goldberg and Triplette 1997) How might different types of aquaculture differ in their effect on fish supply, fisheries, and global food supply? With seaweed, this is NPP that probably would not be available to us without farming, or it would be available to us only via relatively inefficient multiple-trophic level. Molluscs are mostly filter feeders and again this is NPP that would probably not be available to us, except indirectly through other fisheries. Crustaceans (mostly shrimp, but some lobsters) are a fishery that really depends on the methods used and the source of feed. They are generally fed a high proportion of wild-caught fish, so no “new” food is being generated. Food is simply being converted from one form to another and, as we know, conversions of energy never take place with 100% efficiency. Finfish also depends on production methods. There are low intensity methods that rely on in-site production (like the asian carp polyculture). There are intermediate intensity methods where in situ production is supplemented with external food and then there are high intensity methods where all feeds are supplied. What are feed made of? The answer to this question has a significant impact on how much NPP it takes to raise a pound of fish. Let’s look at two important US examples Catfish (Ictalurus punctatus, theChannel Catfish) Salmon (Salmo salar, Atlantic salmon) Salmon Data (1997, From Naylor et al.) Production Percent fish (kTonnes, produced w/ Percentage Percent Percent of Feed or g x Formulated fish meal in fish oil fish feeds not Conversion 10^9) Feeds feeds in feeds of fish origin Ratio Salmon 737 100 45 25 30 1.5 Salmon Calculation Ratio of Fish in Total Feed To Fishmeal Production Produce Fish to Fish Using From Produced Formulated Formulated Total Fish Meal In Total Fish Harvested to With Fish Feeds Feeds Feed Produce Fish Meal Meal Salmon 737 737*1.5 = 1105.5 45% * 1105.5 = 497.5 (15/16)*497 * 5= 2331.9 3.16 Production From Formulated Feeds = All Production Feed needed = Production * Feed Conversion Ratio Fish Meal in Feed = Total Fish Meal * % fish meal in feed Fish harvested to produce fish meal Fish harvested tto produce fish meal is based on 1/6 of fishmeal being a byproduct of other fish processing, and an approximate 5:1 ratio between live fish biomass and fish meal produced. Catfish Data Production Percent fish (kTonnes, produced w/ Percentage Percent Percent of Feed or g x Formulated fish meal in fish oil fish feeds not Conversion 10^9) Feeds feeds in feeds of fish origin Ratio Catfish 428 82 10 3 87 1.8 Catfish Calculations Ratio of Fish in Total Feed To Fishmeal Production Produce Fish to Fish Using From Produced Formulated Formulated Total Fish Meal In Total Fish Harvested With Fish Feeds Feeds Feed to Produce Fish Meal Meal Catfish 350.96 631.728 63.1728 296.1225 0.84 So… Salmon aquaculture consumes more fish than it produces, while catfish aquaculture produces a bit more fish than it consumes. What are the policy implications of this? The implication of the original Science paper (and the similar paper in your reading packet) was that aquaculture is a loosing game, from a biophysical perspective. Let’s take a moment to question that conclusion. We harvest lots of terrestrial NPP directly, but we primarily harvest marine NPP indirectly. Wild-caught fish feed “higher on the food chain” than do farm fish. We can imagine some alternative worlds. In the status quo, aquaculture provides a bit less than 1/5 of the total global fish consumed. Alternatively, all fish that is currently converted to fishmeal is instead fed directly to humans. Another alternative would have us eating high quality high value wild caught fish exclusively and not eating any high value farmed fish. Or, instead of fish, we could eat land animals. How can we compare these alternatives? One possibility: lets look at the approximate “sea footprint” and “land footprint” of each production method. We could need to calculate the approximate NPP for fish and land animals produced each way. For farmed animals we look at what they are fed, break it down into fishmeal and grains (we assume that any fish oils used are byproducts of fishmeal production and this do not take any more fish). How much NPP does it take to produce that grain? How much NPP does it take to produce the fish that are the source of the fishmeal? There are several conversion factors along the way Fish live weight to fish biomass Assume 70% of weight is water, so 30% is biomass (following Spherical Cow). Grain weight to grain biomass Assume 20% of grain by weight is water (following Vitousek et. al. Since this is grain in fish meal, this may not be reasonable. Fish Biomass to NPP Species Main Foods Estimated Trophic Level Peruvian Anchoveta Phytoplanton/zooplankton 2.7 Chilean (Japanese?) Jack Mackerel Zooplanton/piscivore 3.4 Atlantic Herring Zooplanton feeder 3.5 Chub Mackerel Zoplankton 3.1 Japanese Anchovy Phytoplankton/Zooplanton 2.7 Round Sardinella Zooplanton 3.2 Atlantic Mackerel zooplanton/piscivore 3.3 European Anchovy 2.9 Menhaden phytoplankton feeder 2.2 Mean (unweighted) 3.00 Assume 3.0 trophic level Grain to NPP (or direct to land area) Assume 1/10th of total NPP is grain Calculations Amount of Feed Fish used Needed Fish to produce Grain Used Per KG Meal Fish Meal Fish Biomass in Feed Grain produced Used (kg live in Feed (kg (approx) Biomass (kg (kg) (kg) weight) OM) (kg) OM) Farmed Salmon 1.5 0.675 3.16 0.955 0.45 0.36 Wild Salmon Farmed Catfish 1.8 0.18 0.845 0.25 1.57 1.25 Wild Catfish Farmed Beef 8 0 8 6.4 Farmed Poultry 2 0.04 0.19 0.06 1.96 1.57 For wild-caught fish Get data on the approximate trophic level on which they feed (available over the internet on a big database called “Fishbase”) Use that to estimate the amount of NPP required to supply the fish with food Use the “canonical” relationship that approximately 10% of production at any trophic level gets transferred to the next trophic level up Since there is no real data basis for the 10% number, you might want to see how things vary if you alter than number.