Points of concern in Sea Duck conservation

Reproductive Strategies ] Fidelity to Areas ] Compensatory Vs Additive Harvest ] Bag Limits ] Biological Considerations ] Cumulative Mortality Factors ] [ The Status of Seaducks ] A Time for Action ] Population Table ] Population Graphs ] Daily News Article ]


The Status of Sea Ducks in the North Pacific Rim:
Toward Their Conservation & Management
(excerpt)

Transactions of the 59th North American Wildlife and Natural Resources Conference 1994

Background

Species and Status

Sea ducks (tribe Mergini after Johnsgard 1960) are the most northerly distributed ducks, and species diversity is greatest in the North Pacific. They exploit a diversity of inshore and offshore marine habitats during the non-breeding season, and their use of habitat during breeding varies from coastal through freshwater wetlands of the tundra and taiga (Figure 1, Appendix 1). non-breeding cohorts frequent marine habitats most of the year. Sea ducks thus are important indicators of the quality of freshwater and marine ecosystems of northern biomes.

Of the 17 species discussed in this manuscript, at least 13 are reported to be declining (Appendix 2). However, the basis for many of those assessments is equivocal because there has been little effort to monitor populations. The efforts to more precisely assess their status point to catastrophic declines (Kertell 1991, Stehn et al. 1993). Conservation problems related to sea ducks have a long history throughout the holarctic. For example, the Labrador duck (Camptorynchos labradorius) became extinct in 1875 (Phillips 1925); common eiders (Somateria mollissima) declined seriously throughout the northern hemisphere (Townsend 1914, Phillips 1925, Doughty 1979); harlequin ducks (Histrionicus histrionicus) experienced declines in Iceland and Greenland (Gudmundsson 1971, Salomonson 1950), and more recently have been designated endangered in eastern Canada (Committee On the Status of Endangered Wildlife in Canada 1990). In Russia, all species of eider and harlequin ducks have been closed to sport hunting since 198 1, and Chinese mergansers, (Mergus squamatus) presently are extremely rare and fully protected, i.e., category one of the red book (Solomonov 1987).

Current issues. Bartonek (1993) noted an increased concern for the status of sea ducks in the Pacific Flyway due to (1) the listing of the spectacled eider (S. fischeri) as a Threatened species throughout its range in the United States (U.S. Fish and Wildlife Service 1993a); (2) the finding that the Alaskan nesting population of the Steller's eider (Polysticta stelleri) warranted listing as a Threatened species; (3) losses of harlequin ducks stemming from the Exxon Valdez oil spill; and (4) inexplicable mortality of scoters (Melanitta spp.) summering in the Gulf of Alaska. This concern, however, has not changed management approaches to most sea duck populations. Sea ducks are subjected to extremely liberal hunting regulations enhanced by a perception of little hunting interest and insignificant harvest rates of this group (Bartonek 1993, Gillelan 1988, Reiger 1987, 1989, U.S. Fish and Wildlife Service 1993b), and management of hunting kill may be lacking (e.g., Seller's eiders in Russia prior to 1981), or seriously compromised by conflicting interests in subsistence and aboriginal use (Kondratyev 1988, Nichols et al. 1988, Wentworth 1993, Wolfe et al. 1990).

Conservation of wildlife species requires a fundamental understanding of population status, mortality and natality in order to make informed decisions. This knowledge is lacking for sea duck population. Here we review aspects of life histories and simulate demography of sea ducks. By developing matrix models to integrate life history parameters we analyze the effects of varied mortality rates on population dynamics. We present recommendations that redirect our approach to the management and protection of sea ducks.

An Ecological Basis For Conservation

Mortality Theories

Compensation. Patterson (1979) highlighted the need for management based on ecological principles, and integrated theories of compensatory mortality with life history patterns. Empirical evidence suggested that hunting and non-hunting mortality may largely be compensatory for the mallard (Anas platyrhynchos), up to some threshold (after Anderson and Burnham 1976); however, that hypothesis has been largely repudiated (see Johnson et al. 1988). Patterson (1979) expressed concerns that the mallard would be used as a "yardstick" with which numerical kill of other species is evaluated. Also, Mortalbano et al. (1987) were concerned that compensatory mortality had become a philosophical cornerstone of regulatory programs for waterfowl. This philosophy condones an approach to management which can result in over-exploitation of species (Bartonek et al. 1984.).

Additivity. Anderson and Burnham (1976) noted that above a certain level, hunting mortality in the mallard must be additive and this "threshold" must be less than the natural mortality rate. Therefore, species with low natural mortality rates are less capable of "compensating" for hunting mortality than species with high mortality rates. Patterson (1979) noted that mallards and canvasbacks (Aythya valisneria) are at opposite ends of the threshold spectrum, i.e., 0.40 and 0. 10 harvest rates, respectively. He therefore emphasized the need for conservative approaches in the management of hunting kill in the diving ducks (also Pirot and Fox 1990, Hochbaum and Caswell 1978).

We expand this suggestion to include sea ducks. Our analyses indicate that sustainable harvest rates may not exceed about 0.03 of the adult population in some sea duck species. Therefore, our perception of the significance of losses to hunter kill will change based on life history patterns for each species.

The r-K Continuum

Life history. Waterfowl span the entire r-K continuum, and sea ducks exhibit extreme K?selection relative to other species of ducks (Eadie et al. 1988). Like seabirds, sea ducks have deferred sexual maturity, low annual recruitment rates to breeding age, variable annual rates of non-breeding by adults and high annual adult survival rates (see Ricklefs 1990). The highly variable environment of the northern marine ecosystem favors a life history strategy of minimized annual investment in reproduction and extended longevity.

Ecological time. Population stability of sea ducks is dependent on high adult survival and a few successful years of reproduction (e.g., Milne 1974, Swennen 199 1). This results in population growth that is stepped, and average annual rates of increase can reach 5 to 10 percent. Considerations of ecological time become important because infrequent Arctic ice event can cause mass mortality for some species (Barry 1968), and/or might affect body condition and fitness of birds (see Goudie and Ankney 1986). Hence, gains in populations during a few decades of favorable environmental conditions likely are important to buffer against extirpation during harsh conditions.

Species sensitivity. Species which maintain population stability through high adult survival are sensitive to increased mortality (Shaw, 1985). In sea ducks, sensitivity is exacerbated by the relatively high proportionate losses of adults in events such as hunting and oil contamination.

Population Modeling

Intrinsic differences. We generated theoretical populations of various species of ducks over a 20-year period (figure 2, Appendix 3). In this exercise, the mallard population increased to over 5,000 females, whereas the harlequin duck population increased to 400 females. It is clear that the ability of these populations to sustain mortality and/or recover from population declines are dramatically different. Johnson et al. (1988) pointed out that modelling is no panacea for waterfowl management, but it helps to consolidate our understanding of population dynamics. Here modelling supports the need for a different approach to the management of sea duck populations.

Demography. We modelled theoretical populations of harlequin ducks using a Leslie matrix approach (Caswell 1989). We incorporated data on harlequin ducks from Iceland (see Bengtson 1972, Bengtson and Ulfstrand 1971, Gardarsson and Einarsson 1991). Our analysis suggests that population stability occurs when adult survival rates are about 0.85 (Figure 3), a level somewhat less than unhunted populations of common eiders in Scotland (see Coulson 1984). An increasing population of harlequin ducks, i.e., 9.3 percent per year at Lake Myvatn, Iceland from 1975 to 1989) (see Gardarsson and Einarsson 1991), was simulated when adult survival rates approximated 0.95.

Adult survival appears to be the main factor influencing population stability for sea ducks (Appendix 4), suggesting that little can be achieved through management of other biological parameters, such as survival and production of young.

Defining Sustainable Mortality

Simulating mortality. Simulated annual kills of harlequin ducks suggest that losses exceeding 3 to 5 percent of the initial adult population are not sustainable (Figure 3). This is similar to our earlier estimates of harvest rate thresholds. This finding highlights the need to reduce mortality on some species of sea ducks in areas where harvest rates are high, such as in Alaska, Newfoundland and the eastern United States (see Wentworth 1993, Reed and Erskine 1986, Goudie 1989, Krohn et a]. 1992, Wendt and Silieff 1986) and where chronic oil pollution is severe (Piatt et al. 1990a, Chadwick 1993).

Estimating mortality. Because minor increments of mortality can negatively affect populations of sea ducks, the estimation of mortality is fundamental for wise management decisions. However, precision in these estimates is lacking. For example, estimates of hunter kill of sea ducks vary by orders of magnitude depending on the approach to sampling hunters (Goudie 1989, Wendt 1989, Wendt and Silieff 1986, Wentworth 1993, Wolfe et al. 1990). Also, actual losses due to oil spill events are thought to be 5 to 10 times the number of observed corpses (see Piatt et al. 1990b, Patten and Crawley 1993). Furthermore, mortality of sea ducks in the North Pacific may be exacerbated through sublethal contamination of food chains (Henny et al. 1991, 1994).

Estimating trends. Managers are reluctant to take action until declining trends can be demonstrated, yet most sea ducks lack sufficient survey coverage for trend analyses (Appendix 2). Trends are difficult to generate for sea ducks because of inherent stochasticity in the populations and high standard errors in aerial survey techniques. It is unlikely that we have the luxury of awaiting such tenuous results. Our simulation corroborate the long recovery time necessary to rehabilitate some stocks (>50 years). Therefore, managers should expect very little change in trend statistics over 5 to 10?year periods.

Conclusions

We suggest that a fundamental realignment of our management of sea ducks is needed. The recent listing under endangered species programs of three species of seaducks in the northern hemisphere suggests that current management practices are inadequate. The poor effectiveness of past management practices stems from a lack of knowledge of the ecology of sea ducks relative to populations of other waterfowl. Because of high sensitivity of sea ducks to very slight changes in adult mortality, we conclude that managers should adopt conservative measures in the management of mortality. In most cases there is insufficient information on which to base wise management decisions, and therefore managers should take a conservative approach because of the slow recovery rate of sea duck populations.

Recommendations

Management

We stress the need for fundamental changes to the current approaches to sea duck management. These include:

(1) Apply sea duck management at a population level which recognizes the existence of high philopatry and discrete geographic sub-populations.

(2) Hunting regulations to reduce or curtail unsustainable annual mortality to adult sea ducks.

(3) Integrate government and subsistence interests to manage spring and summer kills of sea ducks at sustainable levels.

(4) Integrate "sport" and "subsistence" kills into collective management actions.

(5) Control chronic oil disposal and catastrophic oil spills in coastal waters.

(6) Identify and protect key habitat areas, and manage them to limit hunting and disturbance, buffer against intertidal and benthic habitat alteration, minimize contamination and pollution.

(7) Integrate data on sea duck distribution with coastal zone management to ensure development activities, such as aquaculture, mariculture, commercial fisheries and oil exploration, are sustainable.

(8) Improve enforcement of existing and future regulations aimed to conserve sea ducks.

(9) Identify and implement monitoring programs of "indicator" species in suitable geographic areas. These should serve to indicate the status of the guild of sea ducks.

Research

Very little is known of the ecology of sea ducks. Some approaches to improve our understanding include:

(1) Review existing literature, and identify information gaps and establish priorities.

(2) Refine data on basic demographics of sea duck populations in order to improve our ability to model population dynamics.

(3) Improve our understanding of the trophic web of the marine ecosystems through further studies of the ecology of sea ducks during molt and winter.

(4) Initiate long-term studies of sea ducks that aim to identify ecological factors controlling the "boom and bust" phenomenon of productivity of young, and the influence of natural mortality that periodically can be catastrophic (e.g., delayed ice break-up and starvation).

(5) Analyze foraging activity and habitat use of seaducks to better understand the species-specific requirements for habitat structure.

Home ] Reproductive Strategies ] Fidelity to Areas ] Compensatory Vs Additive Harvest ] Bag Limits ] Biological Considerations ] Cumulative Mortality Factors ] [ The Status of Seaducks ] A Time for Action ] Population Table ] Population Graphs ] Daily News Article ]

 

 

Alaska Wild Animal Recovery Effort
Box 170, Homer, AK 99603
907-235-3877 (FAX) 907-235-5330
E-mail: bear@alaska.net