The Status of Sea Ducks in the North
Toward Their Conservation & Management (excerpt)
Transactions of the 59th North American Wildlife
and Natural Resources Conference 1994
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
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
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
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
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.
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
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
(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.
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
(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
(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
(5) Analyze foraging activity and habitat use of seaducks to better
understand the species-specific requirements for habitat structure.