Posts Tagged ‘faunal analysis’

Identifying and Explaining Intensification in Prehistoric Fishing Practices III: Identification of the Fishing Gear Used from the Size-Frequency Distribution of Fish

September 16, 2009

The previous post concluded that intensification of fishing could be identified from the kind of gear used to capture those fish. Having decided that fish bone assemblages should be subdivided based on the gear used to capture the fish, the issue then becomes: how can we identify that gear? Answering this question requires middle-level theory that can link physical characteristics of the fish assemblage to gear type.

Gear types differ in the sizes of fish that can be captured by them. Nets should capture a larger range of fish sizes than other gear such as hook and line or spear. Hook and line or spears can not effectively capture smaller species. Assemblages formed primarily from net-caught fish should have a larger proportion of small fish than those assemblages that formed from fish primarily caught by hook and line or spear. To verify this intuition, additional sources of data from which middle-level theory could be derived would be very helpful.

Baseline data on the size-frequency distribution of fish from nearshore ocean habitats, drawn from modern sources, could be compared to the size- frequency distribution of fish bone from archeological assemblages. Prehistoric fishers presumably selected a portion of the natural range of variation in fish size through their use of particular fishing gear. Thus, the comparison would facilitate the identification of such selection. Published modern data of this sort are surprisingly rare. Beach seine netting around an estuary in Alaska produced fish assemblages whose size-frequency distributions were largely unimodal with a long tail to the right. The size-frequency distribution of individual species varied from unimodal to multimodal, depending on the number of age-classes present. The applicability of these data as an analogy to fish from my study area can obviously be questioned. I don’t have any reason to believe that the form taken by the Alaskan size-frequency distributions is exceptional, however, and a consideration of the factors that produced these distributions may be useful.

Any nearshore habitat will likely contain a range of species, each represented by specimens from one or more age classes. Different species will vary in mean size within a particular age class. The aggregate of the individual size-frequency distributions is therefore likely to produce a highly variable unimodal distribution, particularly when individuals from many different species are represented. Assemblages formed from a mix of fish caught by net and fish caught by hook and line or spears should have a bimodal size-frequency distribution. The proportion of fish in each mode should reflect the emphasis placed on netting and other fishing gear. Variation in the size-frequency distribution among archeological assemblages should provide some indication of variation in the techniques used to take fish.

© Scott Pletka and Mathematical Tools, Archaeological Problems, 2009.

Identifying and Explaining Intensification in Prehistoric Fishing Practices II: Determining What to Measure and Figuring Out What It Means.

September 15, 2009

In the previous post in this series, I suggested that we needed a way to take observations on archaeological data like fish bone and to determine what those observations implied about how hard people worked. The intellectual machinery used for this transformation is called middle-level theory by archaeologists. Well-justified middle-level theory is essential for archeological interpretation. It directs attention to the kinds of observations that archeologists need to make, and it makes those observations meaningful. For these reasons, I will dwell extensively on the development of some appropriate middle-level theory for the identification of intensified fishing.

Middle-level theory can come from a variety of places. Sometimes archaeologists can conduct experiments to understand what kind of material will be left as a result of particular activities. Historic or modern observations on people engaged in daily activities similar to those activities expected to have occurred in the past are often another useful source. Such observations will be important for the interpretation of fish bones. Middle-level theory can also come from established physical principles. I will also call upon a few physical principles to interpret the fish bones examined in this study.

An ideal source of middle-level theory would be data on the return, in calories, for finding, capturing, and processing different fish species. Fish bone in an archeological collection could then be sorted by their return rate and the effort expended to capture such fish could be quantified. Unfortunately, no comprehensive database of such return rates exists. Ethnographic and archeological data from my study area indicate that fishers took a wide variety of fish from a range of habitats using several different types of gear. The ethnographic data does not provide any basis for quantifying return rates. Experimental evidence on return rates would also be very difficult to acquire, given the large number of fish, habitats, and gear involved. Ethnographic evidence from elsewhere indicates, however, that gear type varies in terms of the amount of work required to manufacture that gear. Hook and line or spears are much easier to make than nets, for example. Sorting and quantifying the amount of fish represented in an archeological collection by the type of gear used to catch them would provide an indication of the effort expended to catch fish. This is the approach that I chose. In the next post, I will describe the methods that I used to determine the type of gear employed by fishers to take the fish in my archeological assemblages.

© Scott Pletka and Mathematical Tools, Archaeological Problems, 2009.

Identification and explanation of intensified prehistoric fishing practices I

September 13, 2009

In this series of posts, I will be exploring ways to identify and explain intensified prehistoric fishing practices. Intensification refers to the input of greater amounts of labor per unit capita to procure resources. As this formal definition implies, people are working harder at subsistence activities when they intensify their way of making a living. How do we determine when people are working harder from archaeological evidence? And what factors would induce people to intensify their efforts?

A lot of theories exist to address the latter question, but the former question is the more immediate problem. We need middle-level theory (sometimes labeled middle-range theory) appropriate to the nature of the archaeological evidence. Middle-level theory links archaeological data to phenomena of interest. It allows archaeologists to say with some confidence what happened in the past, based on that evidence.

My evidence comprises collections of fish bones and other artifacts from an organic-rich trash dump at a single archaeological site. Such trash dumps are often called middens. The occupation of the site spans several hundred years. The trash dump, however, has been sufficiently undisturbed since it was deposited that it could be excavated to recover evidence representative of much shorter spans of time. The mathematical tools that I found useful as I developed appropriate middle-level theory for this evidence included regression analysis, mixture models, and maximum likelihood models. In the next post, I will begin to develop the middle-level theory in detail, talking about the blind alleys down which I went, mistakes that I made, and solutions at which I arrived. Check back soon.

© Scott Pletka and Mathematical Tools, Archaeological Problems, 2009.