There’s enough on this planet for everyone’s needs, but not enough for everyone’s greed Gandhi

Overexploitation Exploitation involves living off the land or sea, using plant and animal products for food, medicine, shelter, fiber, and other products It is the second most important threat to the survival of birds, plants, and mammals It is also the 3 rd most important threat to freshwater fish extinctions

History of Overexploitation Humans have always been ‘extractive’ by nature and ‘primitive’ societies still largely follow this MO While much of this appears sustainable, archaeological and paleontological evidence suggests premodern people have been driving species to extinction for 1,000’s of years

History of Overexploitation Human colonization onto uninhabited islands or continents has typically been followed by mass extinction events of large-bodied vertebrates (e.g. Europe, parts of Asia, N and S Am, Madagascar and many Pacific islands We have awesome potential to kill (e.g. Passenger Pigeon, bison, and the Pau- Brasil tree)

History of Overexploitation Exploitation of plants and animals is a large interest not just in developing countries, but everywhere In the US, it is estimated hunting generates 700K jobs and has an economic impact of $61B (1%)

History of Overexploitation Impacts of Exploitation Most activities are directed at a single target species

Exploitation of Target Species Tropical Terrestrial Ecosystems Timber extraction is a major threat Approximately 5.8M ha of tropical forests logged each year (25% world) Single species approaches (e.g. mahogany) are difficult to compare to other methods, but it is better than clear cutting

Exploitation of Target Species A discrepancy between high inflation and slow growth rate of tree value creates the situation where cutting all trees irrespective of age is the best economic plan

Exploitation of Target Species Subsistence Hunting has been around for more than 100K yrs, but consumption has greatly increased Impact varies tremendously across the tropics E.g. Sarawak (25K ton), Amazon ( K ton), C Af (1-3.7M ton) Much of this is too high (e.g. C Af is 6x higher than sustainable rates)

Exploitation of Target Species Hunting rates are unsustainably high across the Congo (solid) and Amazon (open). Extraction rate Sustainable Rate (20%)

Exploitation of Target Species Subsistence game hunting affects the structure of tropical forest mammal assemblages, as well as other groups through potential cascading effects

Exploitation of Target Species Nontimber forest products (NTFP) E.g. fruits, nuts, oil seeds, latexes, resins, gums, medicinal plants, spices, dyes, fibers, and may others The ethnobotanical studies have catalogued the wide variety of plants used by different groups (e.g. India, 6Kof 16K angiosperms used for traditional medicines, 79% of trees in 1ha of Amazon utilized)

Exploitation of Target Species The traditional view of NTFP is usually assumed to be sustainable and is viewed as a promising alternative to exploitive practices and/or landclearing Extractive reserves are one of the of the fastest growing categories of protected areas in tropical forests The sustainability of these areas is not fully understood at this time

Exploitation of Target Species However, in tropical rural areas, the combined value of consumption and sale of forest goods may not make them sustainable over longer time periods A boom in homeopathic remedies has resulted in >150 sp of European plants becoming endangered and extirpation of many local populations

Exploitation of Target Species Another potential problem is the impact of harvesting on demographic processes and structure Overharvested populations will succumb to demographic collapse

Exploitation of Target Species Forestry Only 22% of the world’s original forest remain in large, relatively natural ecosystems Most are either boreal (48%) or tropical (44%), with only a fraction of temperate forests remaining (3%) Many are currently threatened from increased pressure from logging

Exploitation of Target Species When commercial forestry expands into previously remote, roadless areas, it typically results in high levels of fragmentation of remaining stands A study of postlogging silviculture on wildlife suggests loss of structure (i.e. snags, woody debris) is particularly important to many species

Exploitation of Target Species In Fennoscandia, 50% of the red-listed species are threatened because of forestry In WA, actively managed forests could support 100% of biodiversity whereas timber management on a 50-yr rotation at the landscape level could support a maximum of 87% Why? Largely structural simplification

Exploitation of Target Species Hunting of large mammals, small game, and waterfowl are also major target species in temperate regions Actively managing to increase game animals has proved wildly successful for many species (e.g. deer 500K to 30M) In TX populations are >3M with 0.5M harvested annually

Exploitation of Target Species Waterfowl provide another resource to manage at high levels In 2001, approximately 19.4M birds taken involving 1.6M hunters While this may provide a skewed view of resources, their habitats frequently aid other species of concern (true of waterfowl, probably not for deer) Alternative source ($) for landowners

Exploitation of Target Species Aquatic systems, especially marine fisheries, have been well monitored Since the 1990’s global catches have leveled off for the first time in history, despite better technology being constantly developed and utilized

Exploitation of Target Species Trends have leveled off (and fallen) with aquaculture increasing in importance

Exploitation of Target Species Wild stocks continue to decline due to poor management E.g. A recent survey of 232 stocks showed 83% over the past 25yrs are on the decline E.g. Canadian cod 99.9% since 1960’s By the way, are fish farms a good alternative to wild caught? Are they more productive?

Exploitation of Target Species There are many species that are targets in the oceans There are several traits that many vulnerable species in common (easy to capture and biologically least productive) E.g. occupy shallow waters, form dense shoals in predictable locations, commercially valuable

Exploitation of Target Species Chinese bahaba is a fish that meets this criteria (frequent byproduct of fishing) Its bladder is popular for medicinal properties (7x gold) Relatively late maturity

Exploitation of Target Species Some of these same traits apply to other groups that make species vulnerable E.g. abalone occur in shallow waters and species have been harvested from most valuable to least…densities have changed from 1- 5K/acre to <1/acre

Exploitation of Target Species Many freshwater taxa are subject to exploitation for food and other reasons In 2000, estimated 8.8M tons of inland fish caught (22.4M ton aquaculture) Economics: in US, estimated 35M spent $38B spent fishing/yr Europe, estimate 21.3M anglers

Exploitation of Target Species Populations of 4/7 sp of salmon (Onchorhyncus) listed as endangered Problem?: Problem: this may be the most visible fish species in the world While wild populations are supplemented with hatchery fish, they quickly show divergence (genetically, phenotypically) from wild populations Overfishing and dams

Exploitation of Target Species Other species are also exploited During 19 th century, M’s of freshwater mussels were collected However, despite brief respite, currently M’s of kg are exported to Asia Currently, pollution, dams, dredging, siltation and invasives In US, currently 72% (of 297) considered endangered with 27 extinct

Impacts of Exploitation on Non-Target Species There are direct effects of exploitation, but there are also indirect effects In addition, there may be damage to the environment, causing changes in ‘biological relationships’ or in landscapes or ecosystem functions

Impacts of Exploitation on Non-Target Species Even logging directed at a single species can ‘puncture’ a hole in the forest Even highly selective logging operations with modest levels of incidental damage to nontarget trees can generate enough structural disturbance by increasing desiccation and dry fuel loads Furthermore, mechanized logging itself triggers surface fires

Impacts of Exploitation on Non-Target Species Can you envision a scenario when loss of large-bodied frugivores may impact forest dynamics? Seedling recruitment is not clear under different levels of hunting pressure… however, in some heavily hunted forest dispersal can decrease by 60% 90% in some forests

Impacts of Exploitation on Non-Target Species In temperate regions, loss of large mammals can have deleterious effects Beavers are ecosystem engineers can dramatically alter the landscape Recently, they are making a comeback Loss of Grizzly bears had cascading effects…increasing elk pop(s) and moose, decreasing riparian habitat, reducing songbird populations

Impacts of Exploitation on Non-Target Species When predators are excluded, some herbivore populations can get extremely abundant, altering plant communities (loss of 95% of a rare orchid in WV due to excessive deer browsing)

Impacts of Exploitation on Non-Target Species Marine fisheries are estimated to have a global by-catch of roughly 27M tons/yr How? Trawl fisheries, drift nets and gill nets Shrimp trawlers (with relatively small mesh size) are estimate to discard 5kg of by-catch for 1kg of shrimp

Impacts of Exploitation on Non-Target Species Is this just impacting fish? 19/21 Albatrosses (attempting to eat baited fish) Can they really be that impactful? Each boat may set 1,000’s of hooks/day with a total of >250M hooks/yr It is estimated that 20K sea turtles are caught in the Mediterranean/yr on hooks Up to 120K sea snakes taken in Aust/yr

Impacts of Exploitation on Non-Target Species We were talking about the impact of exploitation on non-target species (e.g. by- catch, albatrosses)

Impacts of Exploitation on Non-Target Species Unfortunately there are many freshwater examples of problems No individuals caught since 2001 May reach 300 kg Only spawn in specific rapids

Impacts of Exploitation on Non-Target Species Indirect freshwater effects Salmon bring a huge nutrient load into freshwater systems as they return to spawn and die (8x inc in macroinverts) Early evidence for a correlation between size of salmon runs from 1924 to 1994 and tree-ring growth rates

Biological Theory to Sustainable Exploitation Density dependent factors impacting the natural rate of increase

Biological Theory to Sustainable Exploitation Why should we think populations to be able to withstand the elevated mortality that occurs with most forms of exploitation? There may be compensatory birth and growth rates to somewhat offset elevated death rates

Biological Theory to Sustainable Exploitation If a large number of individuals are going to die from one time to the next, is ‘thinning’ the equivalent? An easy way to approach the question of elevated mortality is to start with the logistic model, which gives the number of individuals at time t as: N t = N max / 1 + ((N max /N 0 ) – 1)e -rt

Biological Theory to Sustainable Exploitation Where N max is the carrying capacity (which is not stable) Sometimes biomass is substituted for population size (B for N). Why? N t = N max / 1 + ((N max /N 0 ) – 1)e -rt

Biological Theory to Sustainable Exploitation Why should we think populations to be able to withstand the elevated mortality that occurs with most forms of exploitation? There may be compensatory birth and growth rates to somewhat offset elevated death rates

Biological Theory to Sustainable Exploitation Why should we think populations to be able to withstand the elevated mortality that occurs with most forms of exploitation? There may be compensatory birth and growth rates to somewhat offset elevated death rates

Biological Theory to Sustainable Exploitation Classic logistic population growth to a maximum pop(n) size

Biological Theory to Sustainable Exploitation The growth of this classic population is What is the relationship N & N max ? Consider if the pop(n) is being exploited at a steady rate, then its rate of change per unit time (dN/dt) will be the difference between its surplus production and the yield (Y) g(N) = rN (1 – N/N max ) dN/dt = rN (1 – N/N max ) - Y

Biological Theory to Sustainable Exploitation Sustainable yield occurs at 50% of maximum pop(n) size…why?

Biological Theory to Sustainable Exploitation Stabilities of exploitation In theory, we have discovered where the MSY occurs Problem?

Impacts of Exploitation on Non-Target Species In terms of simple population dynamics, it is the ‘surplus’ that can be removed in any given year Depending upon population size, that will vary greatly

Biological Theory to Sustainable Exploitation MSY occurs at intermediate pop(n) size

Biological Theory to Sustainable Exploitation Stability of Exploitation There is a theoretical number of individuals taken…any problems? Lots… –People rarely do as they are told –Conditions do not always favor optimal growth

Biological Theory to Sustainable Exploitation Constant Quotas Constant quotas are determined when the number of individuals removed is independent of the population size (another way to think…subtract Y from the surplus yield, rather than making Y proportion to N) This has been used to set many fishery quotas (e.g. Peruvian anchovies) Is this a good approach?

Biological Theory to Sustainable Exploitation Consider 3 levels of constant quota harvest (no relationship to N) High Quota …will always crash MSY Quota …even when above NMSY, pop(n) will decline Finally, even Low Quota will decline if initial pop(n) is low

Biological Theory to Sustainable Exploitation Proportional exploitation (constant effort) This approach ties ‘takes’ to pop(n) size As long as the exploitation rate is below the intrinsic rate of natural increase, r, then all equilibria are stable Has been shown to be important in tracking actual ‘take’ rates and the importance of monitoring pop(n) sizes

Biological Theory to Sustainable Exploitation Consider the size of the yield (Y), the exploitation rate (E) and the population size. Y = EN (proportional exploitation) Substituting… rN (1 – N/N max ) = EN And as long as E<r then N = N max (1- E/r) g(N) = rN (1 – N/N max )

Biological Theory to Sustainable Exploitation As long as E < r, all equilibria are stable

Biological Theory to Sustainable Exploitation How do the two approaches compare? Examine data from Marten harvests Both approaches do relatively well at low rates

Biological Theory to Sustainable Exploitation Threshold Exploitation involves the use of pop(n) size thresholds to determine not only the rate of exploitation but also whether exploitation should take place at all Since all pop(s) fluctuate, it is this excess that will be harvested If a surplus does not exist, no take will be made (i.e. very safe approach)

Comparison of Approaches to Sustainable Yields There are many approaches to determining what approach should be established for sustainable yields Various strengths and weaknesses (think of a demographic model with all the parameters)

Comparison of Approaches to Sustainable Yields Surplus Production models are also called surplus yield models or “production” models Frequently used in fisheries If you know how yields have responded to different levels of exploitation effort over time, then you could estimate the dome-shaped yield curve (thus not requiring new data)

Comparison of Approaches to Sustainable Yields

There are many pitfalls with this approach including it treats all years as replicates –Consider Cod The largest fisheries collapse ever (Peruvian anchovy) in the early 1970’s when it adopted a surplus production model that suggested levels were safe

Comparison of Approaches to Sustainable Yields Yield-per-recruit models were developed originally as part of the “dynamic pool” concept in the landmark fisheries book written by Beverton and Hold (1957) The dynamic pool attempts to keep track of separate processes that add to a population (e.g. recruitment and growth) or subtract from it (e.g. natural and catch mortality)

Comparison of Approaches to Sustainable Yields Imagine a species that becomes more valuable as it ages If exploitation is weak, most of the fish or trees will be large when taken If you wait too long, natural death occurs This model searches for the level of mortality that maximizes the yield under this tradeoff between numbers and value

Comparison of Approaches to Sustainable Yields Once the level of mortality has been found that maximizes the yield per recruit, we can calculate the total yield that will be obtained from a given level of mortality, if we know how many recruits are coming each year This approach is used in many countries Does require info about how the value (often size) of individuals increases with age, as well as an estimate of natural mortality rates

Comparison of Approaches to Sustainable Yields For some species ($ or conservation) there is enough data for full-blown population models These models combine data on all demographic parameters (survival, age at maturity, age-specific mortality)

Comparison of Approaches to Sustainable Yields Assessment of population growth rates is a common practice to deduce whether populations are declining as a result of direct exploitation or exploitation of their habitats Another use is to diagnose the reasons for population declines and to suggest the likelihood of success of various management strategies (e.g. loggerhead turtles, eggs vs. older adults)

Comparison of Approaches to Sustainable Yields Projected annual strandings for Kemp’s ridley seas turtles under levels of compliance by shrimpers (current to full compliance)

Comparison of Approaches to Sustainable Yields Adjustments based on recent results If we can monitor either the population itself or the numbers of individuals taken, we can adjust the quotas each yr based upon new information This is currently the approach for waterfowl and mammal hunting in the US (read Box 8.1 on martens)

Comparison of Approaches to Sustainable Yields Demographic rule of thumb Parameter-dependent models are useless for the vast majority of the world’s exploited species…why? One of the best-known rules of thumb models to determine if exploitation of tropical mammals can be sustainable It assumes maximum potential production (P max ) occurs at about 60% of K P max = (0.6D x λ max) – 0.6D

Comparison of Approaches to Sustainable Yields Of course there are many potential problems with this simplistic model There are problems with cull rates compared to mortality rates…why? Are density estimates accurate? Why? Estimating λ max is not easy and variable

Comparison of Approaches to Sustainable Yields There are spatial and temporal problems of establishing accurate production numbers

Comparison of Approaches to Sustainable Yields

Overexploitation